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Synthesis of organic molecule donor for efficient organic solar cells with low acceptor content
Accepted Manuscript Synthesis of organic molecule donors for efficient organic solar cells with low acceptor content Kun Wang, Zhuo Xu, Yuan Geng, Hui Li, Chunlei Lin, Liwei Mi, Xia Guo, Maojie Zhang, Yongfang Li PII:
S1566-1199(18)30521-4
DOI:
10.1016/j.orgel.2018.10.006
Reference:
ORGELE 4922
To appear in:
Organic Electronics
Received Date: 30 July 2018 Revised Date:
7 September 2018
Accepted Date: 6 October 2018
Please cite this article as: K. Wang, Z. Xu, Y. Geng, H. Li, C. Lin, L. Mi, X. Guo, M. Zhang, Y. Li, Synthesis of organic molecule donors for efficient organic solar cells with low acceptor content, Organic Electronics (2018), doi: https://doi.org/10.1016/j.orgel.2018.10.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Graphic Abstract Synthesis of Organic Molecule Donor for Efficient Organic Solar Cells with Low Acceptor Content
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Kun Wang,*a Zhuo Xub, Yuan Geng,a Hui Li,a Chunlei Lin,a Liwei Mi,a Xia Guo,*b
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SC
Maojie Zhang*b and Yongfang Lib
A new planar A-D-A structured organic molecule, BDTDPTz, was designed and
EP
synthesized for the application as donor material in organic solar cells (OSCs). The OSCs based on BDTDPTz:PC71BM with a weight ratio of 1.5:1 and 0.25%
AC C
1-Phenylnaphthalene treatment exhibit higher power conversion efficiency (PCE) of 6.28%. The optimized PC71BM content of 40% is one of the lowest acceptor content in the active layer reported so far for the high photovoltaic performance OSCs, and BDTDPTz
could
be
solution-processable OSCs.
promising
high
performance
donor
materials
in
ACCEPTED MANUSCRIPT
Synthesis of Organic Molecule Donors for Efficient Organic Solar Cells with Low Acceptor Content Kun Wang,*a Zhuo Xub, Yuan Geng,a Hui Li,a Chunlei Lin,a Liwei Mi,a Xia Guo,*b
a
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Maojie Zhang*b and Yongfang Lib
School of of Materials and Chemical Engineering, Zhongyuan University of
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Technology, Zhengzhou 451191, China
b
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E-mail: [email protected]
Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical
Engineering and Materials Science, Soochow University, Suzhou 215123, China
Abstract:
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E-mail: [email protected], [email protected]
A new planar A-D-A structured organic small molecule semiconductor (O-SMS) with
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dialkyl-thiophene substituted benzodithiophene (BDT) as central electron-rich core
AC C
flanked by relatively electron-deficient units of [1,2,5]thiadiazolo[3,4-c]pyridine (PTz) and terminated with alkyl-bithiophene as π-conjugated end-caps, BDTDPTz, was designed and synthesized for the application as donor material in organic solar cells (OSCs). BDTDPTz possesses wider absorption spectra with an optical bandgap of 1.65 eV, lower the highest occupied molecular orbital (HOMO) energy level of -5.42 eV and highly crystalline structures in solid films. The OSCs based on BDTDPTz:PC71BM blend film with a lower PC71BM content of 40% demonstrate a 1
ACCEPTED MANUSCRIPT power conversion efficiency (PCE) of 6.28% with a relatively higher open-circuit voltage of 0.868 V and short circuit current density of 12.83 mA cm–2. These results indicate that highly coplanar and crystalline structure of BDTDPTz can effectively
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reduce the content of fullerene acceptor in the active layer and then enhance the absorption and PCE of the OSCs.
Keywords: organic solar cells, organic small molecular donor materials,
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[1,2,5]thiadiazolo[3,4-c]pyridine, benzodithiophene, low acceptor content.
1. Introduction:
Solution-processable bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted broad interests due to their potential applications in next-generation
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lightweight and flexible solar cells, via low cost solution coating technologies and large area printing [1-5]. Active layer of the OSCs is composed of a p-type conjugated polymer [6-8] or organic small molecule [9-11] as donor blending with a fullerene
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derivative [12,13] or a nonfullerene n-type organic semiconductor [14-17] as acceptor.
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BHJ becomes a widely used system in the field of organic photovoltaic because it can form a bicontinuous interpenetrating network which composed by the electron donor and acceptor materials [1]. The bicontinuous interpenetrating network enhances the donor/acceptor interfacial area available for exciton dissociation and thus reduces the distance the exciton needs to travel before reaching an interface [2f]. For the acceptor, fullerene derivatives, such as [6,6]-phenyl-C61-butyric 2
ACCEPTED MANUSCRIPT acid-methylester, [6,6]-phenyl-C71-butyric acid-methyl-ester (PC71BM) and indene-C60 bisadduct ICBA are the most investigated acceptor due to their high electron affinity and excellent electron transport ability. On the other hand, for the donor, especially
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the organic small molecule (O-SM) containing a central electron-rich core flanked by relatively electron-poor units and terminated with π-conjugated end-caps, was regarded as one of the most successful organic small molecular semiconductor
SC
(O-SMS) frameworks due to the powerful photoelectric conversion efficiency (PCE)
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could be almost comparable to that of polymers [18,19].
In our previous work [20], we have synthesized a O-SMS donor material named as BDT-BTF for fullerene-based OSCs. BDT-BTF exhibits a slightly wider bandgap of 1.78 eV with the maximum absorption peaks (λmax) of 643 nm, a moderate highest
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occupied molecular orbital (HOMO) energy level of −5.20 eV, and a high hole mobility (µh) of 1.07×10−2 cm2 V−1 s−1. As a result, the BDT-BTF:PC71BM-based OSCs exhibit a satisfactory PCE of 5.88% with a low fullerene acceptor content of
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25%, an open-circuit voltage (Voc) of 0.85 V, a short circuit current density (Jsc) of
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10.48 mA cm−2, and a fill factor (FF) of 66%. Benzo[1,2-b:4,5-b’]dithiophene (BDT) was used as the central electron-rich core because it has a symmetric and planar conjugated structure and the compact stacking and coplanar molecule can be expected for the BDT-based materials. And the BDT unit has also proved to be one of the most famous building blocks for constructing both conjugated polymer and O-SMS materials in OSCs [21]. In addition, the absorption spectra, molecular energy levels and mobilities of the BDT-based organic semiconductors can be highly tuned by 3
ACCEPTED MANUSCRIPT modifying the functional substituents in the BDT unit [22,23]. For further enhancing the performance of this kind of materials, we selected [1,2,5]thiadiazolo[3,4-c]pyridine (PTz) unit with stronger electron-withdrawing
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ability as acceptor unit [24]. Furthermore, good film-forming characteristics is one of the essential properties of O-SMS, hence, we adopted dialkyl-thiophene side chain on BDT unit as the donor building block.
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To take the advantages of the synergistic strong electron-withdrawing ability of the
film-forming
organic
molecule
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backbone of PTz units and dialkyl-thiophene side chain on BDT unit, a good donor
material
namely
BDTDPTz
with
A-D-A-structure was synthesized and applied as donor material in OSCs. BDTDPTz film shows stronger and wider absorption, low-lying HOMO energy level, better
BDTDPTz:PC71BM
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film-forming and stronger crystallinity compared with BDT-BTF. The OSCs based on film
at
a
D:A weight
ratio
of
1.5:1
with
0.25%
1-Phenylnaphthalene (PN) treatment exhibit higher PCE of 6.28% with a high Voc of
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0.868 V, Jsc of 12.83 mA cm–2 and FF of 56.4%. The OSCs with 40% PC71BM content
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is one of the lowest optimized content of fullerene acceptor in OSCs reported so far. We also investigated the optimized photovoltaic performance of OSCs by the measurements of photoluminescence spectra, light intensity dependence of Jsc values and active layer morphology analysis. The results demonstrated that BDTDPTz could be promising high performance donor materials in solution-processable OSCs.
2. Experimental Section All chemicals and solvents were reagent grades and purchased from J&K, Aldrich and 4
ACCEPTED MANUSCRIPT Alfa Aesar. Monomers BDT and PTz were purchased from Solarmer Materials Inc. and SunaTech Inc., respectively. The detailed synthetic processes of the organic molecule and the detailed fabrication and characterization of the OSC devices were
C8H17
S
S
N
N
S SnMe3 + Br
Me3Sn S
S
S C8H17
C6H13
PTz
C8H17
BDT
C8H17
C8H17
S
N
C6H13
N
S
S
N
S
S
N
S
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S
Pd(PPh3)4 24 h
S
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N
Toluene 110 oC
SC
C8H17
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described in Supporting Information (SI).
N
S
C6H13
N
S C8H17
BDTDPTz
EP
C8H17
S
AC C
Scheme 1. Synthesis route and molecular structure of BDTDPTz. 3. Results and Discussion The synthesis route and chemical structure of BDTDPTz are shown in Scheme 1. The molecular structure was confirmed by 1H Nuclear Magnetic Resonance (1H NMR) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS), as shown in Fig. S1 and Fig. S2 in SI. The acceptor of PC71BM is commercially available. The donor material BDTDPTz was prepared by stille 5
ACCEPTED MANUSCRIPT coupling reaction, and the detailed synthetic processes were described in SI. BDTDPTz exhibits excellent solubility in common organic solvents, such as chloroform, toluene, chlorobenzene, o-dichlorobenzene, etc. BDTDPTz shows broad
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and strong optical absorption in the wavelength range from 300 to 750 nm. Density functional theory (DFT) was employed to gain further insight into the molecular coplanarity and calculate the frontier molecular orbitals surfaces (HOMO and Lowest
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Unoccupied Molecular Orbital (LUMO)) of the optimal geometries for BDTDPTz at
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the B3LYP/6-31G (d, p) level, as shown in Fig. S3 in SI. The calculated HOMO and LUMO energy levels of BDTDPTz are −4.81 eV and −3.03 eV, respectively. The molecular orbital distributions as shown in Fig. S3 (a) and (b) indicate that the HOMO of BDTDPTz was delocalized along the whole π-conjugated backbone of the
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molecule while its LUMO is mainly localized on the PTz-based acceptor segment of BDTDPTz and partially extend along the skeleton of the BDT units. The dihedral angles between the BDT unit and the thiophene unit in side chain is 54.57 º(Fig.
EP
S3(c)). BDTDPTz shows a linear coplanar molecular skeleton conformation from the
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sideview (Fig. S3(d)), which is beneficial for intermolecular π-π stacking.
Normalized Absorption (a.u.)
3.1 UV-Vis Absorption Spectra and Electronic Energy Levels
1.4 1.2
in solution in film
(b)
(a)
1.0 0.8 0.6 0.4 0.2 0.0 300
400
500 600 700 Wavelength (nm)
800
-1.5
6
-1.0 -0.5 0.0 0.5 1.0 + Potential (V vs Ag/Ag )
1.5
ACCEPTED MANUSCRIPT Fig. 1. (a) UV-Vis absorption spectra of BDTDPTz in chloroform solution and solid films; (b) cyclic voltammograms of BDTDPTz film on the glassy carbon electrode in 0.1 mol L−1 Bu4NPF6 in acetonitrile solution at a scan rate of 50 mV s−1. UV-Vis absorption spectra of the solutions in chloroform and the solid thin film of
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BDTDPTz were shown in Fig. 1 (a). BDTDPTz exhibits λmax at 597 nm in chloroform solution with a shoulder peak at 533 nm. From solution to solid state thin film, the absorption spectra of BDTDPTz shows distinctly red-shifts, with a
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concomitant more intense peak at 683 nm, implying that BDTDPTz should have
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strong intermolecular π-π interaction in solid state. The absorption edge (λedge) of BDTDPTz film is at 750 nm, corresponding to an optical bandgap of 1.65 eV. It's worth noting that either λmax or λedge of BDTDPTz (both in solution and solid film) had a red-shifted absorption than its analogue BDT-BTF we reported before [20], the
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correlation data were collected in Table 1. The broad absorption of BDTDPTz is beneficial for achieving a higher Jsc in the OSCs devices. The absorption profile of
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BDTDPTz:PC71BM blend films are presented in Fig. S4 in SI. The HOMO and LUMO levels of BDTDPTz were determined by the cyclic
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voltammogram (CV) measurement as shown in Fig. 1(b). The CV results indicate that the HOMO and LUMO energy levels of BDTDPTz are −5.42 eV and −3.65 eV, respectively. Both the HOMO and LUMO energy levels of BDTDPTz has down-shifted compared with the donor material of BDT-BTF, the correlation data were collected in Table 1. These data suggest that BDTDPTz was appropriate for the application as donor materials with PC71BM acceptor in photovoltaic devices. What is more, the deep HOMO energy level of BDTDPTz is beneficial for achieving a higher 7
ACCEPTED MANUSCRIPT Voc in the OSCs devices based on BDTDPTz as donor material. The relevant optical and electrochemical parameters were collected in Table 1 for a clear comparison. Table 1 Optical, electrochemical and thermochemistry properties of BDTDPTz Td (°C)
a
Material
Tm (°C)
Tx (°C)
λmax (nm) Sol.
λmax (nm) film
BDTDPTz
433
213
199
597
683
1.65
-5.42
-3.65
BDT-BTF
425
213
196
559
643
1.78
-5.20
-3.4220
Egopt (eV)
d
HOMO (eV)
e
LUMO (eV)
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c
Tm = endothermic peak; bTx = exothermic peak; cEgopt=1240/λedge; dHOMO = -e (φox +
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4.71) (eV); eLUMO = -e (φred + 4.71) (eV).
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a
b
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3.2 Optical-to-Electrical Conversion Process
Fig. 2. Molecular energy level diagrams of BDTDPTz and PC71BM.
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The process of optical-to-electrical conversion process in the blend film can be summarized in a series of sequential steps as follows: 1) Absorption of a photon generates the exciton; 2) Exciton diffusion to the donor/acceptor interfaces; 3) Charge transfer i.e. exciton disscociation into a free electron and hole pair; 4) Charge collection at the corresponding electrode [1b]. The molecular energy levels of the active layer materials play an important role in optical-to-electrical conversion process. As shown in Fig. 2, the molecular energy levels of BDTDPTz and PC71BM 8
ACCEPTED MANUSCRIPT displayed a larger ∆EHOMO (EHOMOdonor−EHOMOacceptor) of 0.45 eV, which would facilitate to obtain a higher Jsc in devices. The ∆ELUMO (ELUMOdonor−ELUMOacceptor) in BDTDPTz:PC71BM pair is 0.26 eV, which provides a powerful driving force for the
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charge separation at the bulk interface. Furthermore, the lower HOMO energy levels of BDTDPTz are beneficial to a higher Voc for the OSCs with the BDTDPTz as donor because Voc of OSCs is related to the difference of the LUMO of the acceptor
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and the HOMO of the donor materials. In addition, the strong crystallinity of
recombination in devices.
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BDTDPTz is beneficial to form favorable blend morphology and hence to suppress
3.3 Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) analysis
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Thermogravimetric analysis (TGA) was used to evaluate the thermal stability of BDTDPTz (Fig. 3(a)), the decomposition temperature (Td) (at 5% weight loss) of
EP
BDTDPTz was approximately 433 °C. The high Td indicates that BDTDPTz has excellent thermal stability in organic optoelectronic devices. The thermodynamic
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properties were analyzed by differential scanning calorimetry (DSC) measurement and the thermograms were obtained from -20 to 300 °C (Fig. 3(b)). BDTDPTz shows an apparent endothermic peak at 213 °C and a clear exothermic peak at 196 °C. According to the DSC analysis, we can find that BDTDPTz molecules have strong crystallizing ability. The relevant thermochemistry parameters were collected in Table 1.
9
ACCEPTED MANUSCRIPT 5 (a)
4
Weight (%)
−1
433 ºC
80 60 40
BDTDPTz
100
200 300 400 500 Temperature (ºC)
(b)
3 2 Cool
1 0 Heat
-1 -2 -3 -50
600
199 ºC
213 ºC
0
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Heat Flow (W g )
100
50 100 150 200 250 300 Temperature (ºC)
Fig. 3. (a) TGA plots of BDTDPTz with a heating rate of 10 °C min˗1 under the
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nitrogen atmosphere; (b) DSC thermogram of BDTDPTz with a scan rate of 5 °C min˗1 under nitrogen atmosphere.
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3.4 Photovoltaic Properties of the OSCs
We optimized the device fabrication process with a structure of indium tin oxide (ITO)/poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) (20 (7
nm)/BDTDPTz:PC71BM/
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nm)/MoO3
poly[(9,9-bis(3′-(N,N-dimethyl)-nethylammoinium-propyl)-2,7-fluorene)-alt-2,7-(9,9dioctylfluorene)]dibromide (PFN-Br)/Al(100 nm). It is noteworthy that, we choose
EP
MoO3 as a thin interlayer between PEDOT:PSS and active layer, mainly because of
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the acidic nature of the PEDOT:PSS, which ultimately results in protonation of the PTz pyridyl nitrogen [25]. Chloroform was applied to prepare the solution for spin-coating the active layer, and to further improve the photovoltaic performance, PN was adopted as the solvent additive. Fig. 4 shows the current density-voltage (J−V) curves of the devices with different donor/acceptor (D/A) weight ratios from 1:1 to 2.5:1 under 100 mW cm–2 AM 1.5G illumination, and Table 2 lists the photovoltaic parameters of the OSCs for a clear comparison.
10
(b) 50
1:1 1.5:1 2:1 2.5:1
-3
40
-6 -9 -12
30 1:1 1.5:1 2:1 2.5:1
20 10
-15 -0.2
0.0
0.2
0.4
0.6
0.8
0
1.0
400
(d)
(c)
60 without 0.25% PN 0.5% PN
50 EQE (%)
-3 -6 -9 -12 -15 -0.2
40
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−2
Current density (mA cm )
70 0
500
600
700
800
Wavelength (nm)
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Voltage (V)
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0
60
(a)
EQE (%)
−2
Current density (mA cm )
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Without 0.25% PN
30 20 10
0
0.0
0.2
0.4
0.6
0.8
Voltage (V)
1.0
400
500 600 700 Wavelength (nm)
800
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Fig. 4. (a) J–V curves and (b) the corresponding EQE curves of the devices based on BDTDPTz:PC71BM blend film with different D/A ratios; (c) J–V curves and (d) the corresponding EQE curves of the devices based on BDTDPTz:PC71BM (D/A = 1.5:1)
EP
active layer with additive of PN.
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The OSCs devices based on BDTDPTz:PC71BM blend film with a D/A ratio of 1:1 (where the content of PC71BM is 50%) exhibits a PCE of 4.11%, accompanying with a Voc of 0.870 V, Jsc of 9.04 mA cm–2, and a FF of 52.3%. When the D/A weight ratio of the blend film increased to 1.5:1, where the PC71BM content decreased to 40%, a higher PCE of 4.98% was obtained, which benefitted from the enhanced Jsc and slightly improved Voc. Further decreasing the content of PC71BM acceptor, the PCE declined to 3.93% for the OSCs with D/A ratio of 2:1 where the PC71BM content is
11
ACCEPTED MANUSCRIPT 33% and 3.15% for the OSCs with D/A ratio of 2.5:1 where the PC71BM content is 28%, respectively, although the OSCs exhibit an almost constant Voc of 0.865–0.874 V. The declined PCE values of the devices were mainly due to the decreased Jsc and
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FF (as shown in Fig. 4(c) and Table 2). The OSCs with the D/A weight ratio of 1.5:1 for our new donor material PBDTBTz-T is one of the lowest optimized content of fullerene acceptor (40%) in OSCs reported in literature so far [26].
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The external quantum efficiency (EQE) spectra of the above-mentioned devices are
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shown in Fig. 4(b). The EQE curves of these devices with different D/A ratio cover a wavelength range from 350-750 nm, which agrees with the absorption spectra of the active layer. When the PC71BM content is 40%, the OSCs displayed a maximum EQE response value of 53.7% at 560 nm.
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Table 2 Photovoltaic parameters of the OSCs based on BDTDPTz:PC71BM with different conditions under the illumination of AM 1.5G, 100 mW cm–2. Voc (V)
Jsc/Jsca (mA cm–2)
FF (%)
PCE (%)
0.870
9.04/8.72
52.3
4.11
0.874
10.96/10.53
51.9
4.98
0.871
9.55/9.06
47.3
3.93
2.5:1
0.865
8.64/8.26
42.1
3.15
1.5:1 (0.25% PN)
0.868
12.83/12.31
56.4
6.28
1.5:1 (0.5% PN)
0.878
10.20
49.0
4.38
1:1 1.5:1
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2:1
EP
D/A ratio
a
Integrated from EQE In order to further improving the photovoltaic performance of OSCs devices, on the
basis of D/A weight ratio of 1.5:1, we examined the role of additives, PN finally was 12
ACCEPTED MANUSCRIPT selected as solvent additive (as shown in Fig. 4(c)). As reported in the literature25, 26a, we are very carefully to adjust the amount of the additive. An optimized PCE of the device reached 6.28% with a Voc of 0.868 V, Jsc of 12.83 mA cm–2, and a FF of 56.4%
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when the additive PN content is 0.25%. The corresponding EQE curves displayed a wide response range in the wavelength region of 350–750 nm with a maximum value of 64.4%, indicating efficient photoelectron conversion in the device. Increasing the
SC
PN content leads to deterioration in performance. The corresponding UV-Vis spectra
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are shown in Fig. S4 in SI.
The current density values calculated from the EQE curves are consistent with those obtained from the J–V measurement with deviation less than 5% (see Table 2), indicating that the J−V measurements in this work are reliable.
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In addition to efficiency, device stability is another important factor influencing the OSCs commercial application. High device stability is a necessary prerequisite for practical applications of OSCs. Here, we tested
EP
the storage stability of the device. However, the result was not
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satisfactory, the PCE of the OSCs dropped to 80 percent of its original value after 48 h of storage in the N2-filled glove box (Figure S6). We thought that the decreased efficiency was mainly caused by the instability of device structure and active layer morphology. 3.5 Photoluminescence Quenching Effect
13
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84.6% 90.8% 800 900 1000 1100 1200 Wavelength (nm)
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@695 nm BDTDPTz D/A=1.5:1 D/A=1.5:1 with 0.25% PN
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Fig. 5. Photoluminescence spectra of BDTDPTz and BDTDPTz:PC71BM blend films (D/A = 1.5:1) with or without PN.
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Photoluminescence (PL) quenching experiment was used to investigate the photoinduced exciton dissociation and charge transfer efficiency in the blend films. According to the maximum absorptions, excitation wavelengths in the PL measurements were selected to be 695 nm. As shown in Fig. 5, the
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BDTDPTz:PC71BM blend film with additive treatment demonstrated more than 90% PL quenching compared to the PL spectra of the pure BDTDPTz, the value is higher
EP
than those of the blends without solvent additive treatment. Higher PL quenching efficiency means that the BDTDPTz:PC71BM blend film with solvent additive
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treatment have an effective photoinduced exciton dissociation and charge transport, which is in agreement with the higher EQE and PCE values of the corresponding OSCs device.
3.6 Carier Mobility In order to better understand the effect of solvent additive on the photovoltaic performance of the OSCs devices, both the hole (with a hole-only device structure, 14
ACCEPTED MANUSCRIPT ITO/PEDOT:PSS/MoO3/Active layer/MoO3/Al) and electron (with an electron-only device structure, ITO/ZnO(gel)/Active layer/ZnO(NPS)/Al) mobilities (µh and µe) of BDTDPTz and BDTDPTz:PC71BM blend films were measured by the space charge
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limited current (SCLC) method as shown in Fig. S5 in SI, and the corresponding data are collected in Table S1 in SI. The µh of the pure BDTDPTz is 2.38×10−4 cm2 V−1 s−1, but the µe of BDTDPTz is too low to be measured. The µh and µe of
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BDTDPTz:PC71BM (with D/A ratio of 1.5:1) blend film are calculated to be 3.44×
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10-5 cm2 V−1 s−1 and 3.29×10-4 cm2 V−1 s−1, respectively, with µe/µh ratio of 9.56. After solvent additive treatment, the µh and µe values of the device were increased to 8.20×10-5 cm2 V−1 s−1 and 3.73×10-4 cm2 V−1 s−1, respectively, with µe/µh ratio of 4.55. Here, we noticed that the unbalance hole and electron mobilities (i.e. µe/µh ratio)
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of the blend film were further expanded compared to BDT-BTF [20], on the other hand, both the hole and electron mobility of the active layer have decreased to a certain extent (<10-4 cm2 V−1 s−1) compared to BDT-BTF [27], thus, a lower FF was
EP
observed in the OSCs. We thought this could be caused by the addition of alkyl side
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chains on the BDT unit.
3.7 Light Intensity Dependence
15
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(a) Without 0.25% PN
−2
Jph (mA cm− )
10
0.1 0.01
0.1
1
0.88 (b)
(c) 0.86
10
0.84
without (S=0.928) 0.25% PN (S=0.957)
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Voc (V)
−2
Jph (mA cm− )
SC
Veff (V)
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1
0.82 0.8
without (1.52 kT /q) 0.25% PN (1.28 kT /q)
0.78
1 10
100 −2 Light intensity (mW cm )
10
−2
100
Light intensity (mW cm )
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Fig. 6. (a) Jph versus Veff characteristics, and dependence of Jph (b) and Voc (c) on light intensity for the OSCs based on BDTDPTz:PC71BM (1.5:1, w/w) with/without solvent additive treatment.
EP
For further understanding the influence of the solvent additive on the exciton
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dissociation and charge collection process of the OSCs, the dependence of the photocurrent (Jph) on the effective voltage (Veff) were measured and analyzed according to our or other group’s reported work [19a,28], as shown in Fig. 6(a). The calculated exciton dissociation probability (Pdiss) under short-circuit conditions is determined by the normalized Jph at the saturated current density (Jsat), i.e. Jph/Jsat ratio [29]. The Pdiss values of BDTDPTz:PC71BM devices (D/A = 1.5:1) without or with PN additive were calculated as 74.2% and 80.8%, respectively, indicating exciton
16
ACCEPTED MANUSCRIPT dissociation and charge collection in the latter device is more efficient than that in the former. The dependence of photocurrent (Jph) and Voc under different light intensities offers
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deeper insight into the influence of additive treatment on recombination process in the OSCs device, as shown in Fig. 6(b). The relationship of Jph and the light intensity (Plight) can be expressed as Jph∝PlightS, where the exponential factor S implies the
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extent of the bimolecular recombination. A linear dependence of Jph on Plight with S
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value close to 1 implies weak bimolecular recombination in the device [30]. For both of the devices without or with PN treatment, the S values were 0.928 and 0.957, respectively, indicating that additive treatment can effectively reduce the occurrence of bimolecular recombination process in BDTDPTz:PC71BM film with D/A ratio of
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1.5:1.
The slope of Voc versus lnPlight can helps us to estimate the degree of trap-assisted recombination in the devices, as shown in Fig. 6(c). The relationship between Voc and
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Plight could be described as Voc∝lnPlight, and the slope of the fitting straight line should
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be kT/q (where q is the elementary charge, k is the Boltzmann constant, and T is the Kelvin temperature) if bimolecular recombination is the exclusive recombination form [31]. In our cases, the device with additive treatment showed a slope of 1.28 kT/q, smaller than the device without PN with a slope of 1.52 kT/q. This result indicates that additive treatment could suppress trap-assisted recombination in the active layer, leading to an improved Jsc. 3.8 Morphology Studies of the Active Layer 17
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Fig. 7. AFM height (a, d) and phase (b, e) images of the blend films of
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BDTDPTz:PC71BM (1.5:1, w/w) without/with solvent additive; TEM images of BDTDPTz:PC71BM (1.5:1, w/w) without (c)/with (f) solvent additive. For further explaining the effect of solvent additive on the photovoltaic
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performance of the OSCs based on BDTDPTz:PC71BM blend film with D/A ratio of 1.5:1, we measured the morphology of the active layers by atomic force microscopy
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(AFM) and transmission electron microscopy (TEM). As shown in Fig. 7, the BDTDPTz:PC71BM film without solvent additive (Fig. 7(a)) has higher surface roughness (Rq) than the blend film with 0.25% PN (Fig. 7(d)), i.e. 3.41 nm versus 1.45 nm, and also the larger granular aggregations can be observed in the former (Fig. 7(b)), implying that the former film has stronger phase separation than the latter (Fig. 7(e)). Large-scale phase-separated morphology (>50 nm) can be clearly seen in the TEM image (Fig. 7(c)), which may cause more geminate recombination and 18
ACCEPTED MANUSCRIPT bimolecular recombination, and thus results in lower Jsc of the OSCs device. Accompanied with solvent additive treatment, the size of the granular aggregates reduced gradually. An appropriate D/A interpenetrating network was observed with
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size of ca. 10~20 nm for the BDTDPTz and PC71BM networks by 0.25% PN treatment (Fig. 7(f)), which indicates that BDTDPTz have a good miscibility with PC71BM in the active layers. The AFM morphologies correlate well with the images
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observed from TEM. The interpenetrating network of the blend films indicates that
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the organic molecules with the molecular structure like BDTDPTz could be forming efficient percolation channels in solution-processable OSCs [20, 26a, 32]. The efficient percolation channels is beneficial for charge separation and transport, thus improving the carrier collection efficiency and leading to a high Jsc, which agrees well
4. Conclusions
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with the optimized photovoltaic performance of the OSCs.
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In conclusion, a new organic molecule with BDT as central donor unit and PTz as acceptor unit, BDTDPTz, was rationally designed and synthesized for the application
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as donor material in OSCs. Compared with BDT-BTF molecule, BDTDPTz with dialkyl side chains on BDT unit and nitrogen-atoms substitution on BT unit exhibits stronger and broader absorption, lower-lying HOMO energy level, good film-forming and stronger crystallinity. The OSCs based on BDTDPTz:PC71BM film at a D:A weight ratio of 1.5:1 with 0.25% PN treatment exhibit higher PCE of 6.28% with a higher Voc of 0.868 V, Jsc of 12.83 mA cm–2 and FF of 56.4% . The OSCs with 40% PC71BM content is one of the lowest optimized content of fullerene acceptor in OSCs 19
ACCEPTED MANUSCRIPT reported so far. The improvement of the photovoltaic performance by additive treatment was studied by the measurements of photoluminescence spectra, light intensity dependence of Jsc values and active layer morphology analysis. Our results
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confirm that the OSCs based on BDTDPTz:PC71BM film with additive treatment possess higher charge separation and transportation efficiency, less charge recombination and good donor/acceptor nanoscale phase separated interpenetrating
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network and, therefore, demonstrated higher photovoltaic performance. However, the
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overall performance of the OSCs device was limited by the lower charge carrier mobility of BDTDPTz. In considering the simple molecular structures of BDTDPTz and the satisfactory photovoltaic performance, as well as the photophysical properties, the A-D-A-type donor materials can be further tuned through molecular engineering
BDTDPTz
could
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on the A or D units, thus, the organic molecules with the molecular structure like be
promising
high
performance
donor
materials
in
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solution-processable OSCs.
ACKNOWLEDGEMENTS
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This work was supported by the National Natural Science Foundation of China (21502134, 51573120 and 51773142), Henan Province Science and Technology Planning Project (182102210530), Zhongyuan University of Technology Youth Backbone Teachers Funding Planning Project and Program for Interdisciplinary Direction Team in Zhongyuan University of Technology, China.
References: 20
ACCEPTED MANUSCRIPT [1] (a) G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789–1791; (b) S. R. Forrest, MRS Bull. 30 (2005) 28-32. [2] (a) S. Günes, H. Neugebauer, N.S. Sariciftci, Chem. Rev. 107 (2007) 1324–1338; 488 (2012)
RI PT
(b) M. Graetzel, R.A. J. Janssen, D.B. Mitzi, E.H. Sargent, Nature
304–312; (c) X. Guo, M. Baumgarten, K. Müllen, Prog. Polym. Sci. 38 (2013) 1832–1908; (d) K.A. Mazzio, C.K. Luscombe, Chem. Soc. Rev. 44 (2015) 78–90; (e)
SC
X. Che, Y. Li, Y. Qu, S.R. Forrest, Nat. Energy, 3 (2018) 422–427; (f) T. M. Clarke,
M AN U
J. R. Durrant, Chem. Rev. 110 (2010) 6736–6767.
[3] (a) Z. He, H. Wu, Y. Cao, Adv. Mater. 26 (2014) 1006–1024; (b) Y.F. Li, Acc. Chem. Res. 45 (2012) 723; (c) Z.-G. Zhang, Y.F. Li, Sci. China Chem. 58 (2015) 192–209.
TE D
[4] (a) L. Lu, T. Zheng, Q, Wu, A.M. Schneider, D. Zhao, L. Yu, Chem. Rev. 115 (2015) 12666–12731; (b) G. Li, W.-H. Chang, Y. Yang, Nat. Rev. Mater. 2 (2017) 17043.
EP
[5] (a) F.C. Krebs, Sol. Energy Mat. Sol. C. 93 (2009) 394–412; (b) N. Espinosa, M.
AC C
Hösel, M. Jørgensen, F.C. Krebs, Energy Environ. Sci. 7 (2014) 855–866; (c) T.R. Andersen, H.F. Dam, M. Hösel, M. Helgesen, J.E. Carlé, T.T. Larsen-Olsen, S.A. Gevorgyan, J.W. Andreasen, J. Adams, N. Li, F. Machui, G.D. Spyropoulos, T. Ameri, N. Lemaître, M. Legros, A. Scheel, D. Gaiser, K. Kreul, S. Berny, O.R. Lozman, S. Nordman, M. Välimäki, M. Vilkman, R.R. Søndergaard, M. Jørgensen, C.J. Brabec, F.C. Krebs, Energy Environ. Sci. 7 (2014) 2925–2933. [6] (a) S.-H. Liao, H.-J. Jhuo, Y.-S. Cheng, S.-A. Chen, Adv. Mater. 25 (2013) 21
ACCEPTED MANUSCRIPT 4766–4771; (b) T.M. Swager, Macromol. 50 (2017) 4867–4886; (c) C. Liu, K. Wang, X. Gong, A.J. Heeger, Chem. Soc. Rev. 45 (2016) 4825–4846; (d) C.H. Cui, W.-Y. Wong, Y.F. Li, Energy Environ. Sci. 7 (2014) 2276–2284; (e) C.H. Cui, Z.C. He, Y.
RI PT
Wu, X. Cheng, H. Wu, Y. Li, Y. Cao, W.-Y. Wong, Energy Environ. Sci. 9 (2016) 885–891; (f) H. Hu, P.C.Y. Chow, G. Zhang, T. Ma, J. Liu, G. Yang, H. Yan, Acc. Chem. Res. 50 (2017) 2519−2528; (g) H. Bin, Z.-G. Zhang, L. Gao, S. Chen, L.
SC
Zhong, L. Xue, C. Yang, Y. Li, J. Am. Chem. Soc. 138 (2016) 4657–4664; (h) M.
M AN U
Zhang, X. Guo, W. Ma, H. Ade, J. Hou, Adv. Mater. 26 (2014) 5880–5885; (i) S. Li, L. Ye, W. Zhao, H. Yan, B. Yang, D. Liu, W. Li, H. Ade, J. Hou, J. Am. Chem. Soc. 140 (2018) 7159–7167.
[7] (a) B. Fan, L. Ying, P. Zhu, F. Pan, F. Liu, J. Chen, F. Huang, Y. Cao, Adv. Mater.
TE D
29 (2017) 1703906; (b) Z.-G. Zhang, Y. Yang, J. Yao, L. Xue, S. Chen, X. Li, W. Morrison, C. Yang, Y. Li, Angew. Chem. Int. Ed. 56 (2017) 13503–13507; (c) I. Osaka, K. Takimiya, Adv. Mater. 29 (2017) 1605218; (d) D. Liu, B. Yang, B. Jang, B.
EP
Xu, S. Zhang, C. He, H.Y. Woo, J. Hou, Energy Environ. Sci. 10 (2017) 546–551; (e)
AC C
W. Zhao, S. Li, H. Yao, S. Zhang, Y. Zhang, B. Yang, J. Hou, J. Am. Chem. Soc. 139 (2017) 7148−7151; (f) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang, J. Hou, Chem. Rev. 116 (2016) 7397–7457; (g) Y. Cui, H. Yao, C. Yang, S. Zhang, J. Hou, Acta Polym. Sin. 2 (2018) 223–230; (h) C. Sun, F. Pan, H. Bin, J. Zhang, L. Xue, B. Qiu, Z. Wei, Z.-G. Zhang, Y. Li, Nat. Commun. 9 (2018) 743. [8] (a) Z. He, B. Xiao, F. Liu, H. Wu, Y. Yang, S. Xiao, C. Wang, T.P. Russell, Y. Cao, Nat. Photonics
9 (2015) 174; (b) S. Nam, J. Seo, S. Woo, W.H. Kim, H. Kim, D.D.C. 22
ACCEPTED MANUSCRIPT Bradley, Y. Kim, Nat. Commun. 6 (2015) 8929; (c) N. Zhou, X. Guo, R.P. Ortiz, T. Harschneck, E.F. Manley, S.J. Lou, P.E. Hartnett, X. Yu, N.E. Horwitz, P.M. Burrezo, T.J. Aldrich, J.T.L. Navarrete, M.R. Wasielewski, L.X. Chen, R.P.H. Chang, A.
RI PT
Facchetti, T.J. Marks, J. Am. Chem. Soc. 137 (2015) 12565–12579; (d) K. Kawashima, Y. Tamai, H. Ohkita, I. Osaka, K. Takimiya, Nat. Commun. 6 (2015) 10085; (e) L. Lu, M.A. Kelly, W. You, L. Yu, Nat. Photonics
9 (2015) 491; (f) T. Liu,
SC
X. Pan, X. Meng, Y. Liu, D. Wei, W. Ma, L. Huo, X. Sun, T. H. Lee, M. Huang, H.
M AN U
Choi, J.Y. Kim, W.C.H. Choy, Y. Sun, Adv. Mater. 29 (2017) 1604251; (g) X. Xu, T. Yu, Z. Bi, W. Ma, Y. Li, Q. Peng, Adv. Mater. 30 (2018) 1703973. [9] (a) N. Qiu, H. Zhang, X. Wan, C. Li, X. Ke, H. Feng, B. Kan, H. Zhang, Q. Zhang, Y. Lu, Y. Chen, Adv. Mater. 29 (2017) 1604964; (b) H. Bin, Y. Yang, Z.-G. Zhang, L.
TE D
Ye, M. Ghasemi, S. Chen, Y. Zhang, C. Zhang, C. Sun, L.-W. Xue, C. Yang, H. Ade, Y. Li, J. Am. Chem. Soc. 139 (2017) 5085–5094; (c) Y. Lin, Y. Li, X. Zhan, Chem. Soc. Rev. 41 (2012) 4245–4272; (d) B. Walker, C. Kim and T.-Q. Nguyen, Chem. Mater.
EP
23 (2011) 470–482; (e) A. Mishra, P. Bäuerle, Angew. Chem. Int. Ed. 51 (2012)
AC C
2020–2067; (f) K. Sun, Z. Xiao, S. Lu, W. Zajaczkowski, W. Pisula, E. Hanssen, J.M. White, R.M. Williamson, J. Subbiah, J.Y. Ouyang, A.B. Holmes, W.W.H. Wong, D.J. Jones, Nat. Commun. 6 (2015) 6013. [10] (a) B. Kan, Q. Zhang, M. Li, X. Wan, W. Ni, G. Long, Y. Wang, X. Yang, H. Feng, Y. Chen, J. Am. Chem. Soc. 136 (2014) 15529–15532; (b) T. Li, T. Meyer, Z. Ma, J. Benduhn, C. Körner, O. Zeika, K. Vandewal, K. Leo, J. Am. Chem. Soc. 139 (2017) 13636−13639; 23
ACCEPTED MANUSCRIPT [11] (a) Q. Zhang, B. Kan, F. Liu, G. Long, X. Wan, X. Chen, Y. Zuo, W. Ni, H. Zhang, M. Li, Z. Hu, F. Huang, Y. Cao, Z. Liang, M. Zhang, T.P. Russell, Y. Chen, Nat. Photonics
9 (2014) 35–41; (b) B. Kan, M. Li, Q. Zhang, F. Liu, X. Wan, Y. Wang, W.
RI PT
Ni, G. Long, X. Yang, H. Feng, Y. Zuo, M. Zhang, F. Huang, Y. Cao, T.P. Russell, Y. Chen, J. Am. Chem. Soc. 137 (2015) 3886–3893.
[12] (a) Y.-Y. Lai, Y.-J. Cheng, C.-S. Hsu, Energy Environ. Sci. 7 (2014) 1866–1883;
SC
(b) S, Kirner, M. Sekita, D.M. Guldi, Adv. Mater. 26 (2014) 1482–1493; (c) S.-H.
M AN U
Liao, H.-J. Jhuo, Y.-S. Cheng, V. Gupta, S.-A. Chen, J. Mater. Chem. A 3 (2015) 22599–22604; (d) Z. Xiao, X. Geng, D. He, X. Jia, L. Ding, Energy Environ. Sci., 9 (2016) 2114–2121.
[13] (a) C. Cui, Y.W. Li, Y. Li, Adv. Energy Mater. 7 (2016) 1601251; (b) Y. Li, Chem.
TE D
Asian J. 8 (2013) 2316–2328; (c) Y. He, H.-Y. Chen, J. Hou, Y. Li, J. Am. Chem. Soc. 132 (2010) 1377–1382; (d) Y. He, G. Zhao, B. Peng, Y. Li, Adv. Funct. Mater. 20 (2010) 3383–3389; (e) X. Meng, G. Zhao, Q. Xu, Z. Tan, Z. Zhang, L. Jiang, C. Shu,
EP
C. Wang, Y. Li, Adv. Funct. Mater. 24 (2014) 158–163.
AC C
[14] (a) W. Jiang, Y. Li, Z. Wang, Acc. Chem. Res. 47 (2014) 3135−3147; (b) F. Würthner, C.R. Saha–Möller, B. Fimmel, S. Ogi, P. Leowanawat, D. Schmidt, Chem. Rev. 116 (2016) 962–1052; (c) Y. Zhong, M.T. Trinh, R. Chen, G.E. Purdum, P.P. Khlyabich, M. Sezen, S. Oh, H. Zhu, B. Fowler, B. Zhang, W. Wang, C.-Y. Nam, M.Y. Sfeir, C.T. Black, M.L. Steigerwald, Y.-L. Loo, F. Ng, X.-Y. Zhu, C. Nuckolls, Nat. Commun. 6 (2015) 8242; (d) J. Zhang, Y. Li, J. Huang, H. Hu, G. Zhang, T. Ma, P.C. Y. Chow, H. Ade, D. Pan, H. Yan, J. Am. Chem. Soc. 139 (2017) 16092–16095. 24
ACCEPTED MANUSCRIPT [15] (a) C. Yan, S. Barlow, Z. Wang, H. Yan, A.K.-Y. Jen, S.R. Marder, X. Zhan, Nat. Rev. Mater. 3 (2018) 18003; (b) Y. Lin, Z.-G. Zhang, H. Bai, J. Wang, Y. Yao, Y. Li, D. Zhu, X. Zhan, Energy Environ. Sci. 8 (2015) 610−616; (c) Y. Lin, J. Wang, Z.-G.
RI PT
Zhang, H. Bai, Y. Li, D. Zhu, X. Zhan, Adv. Mater. 27 (2015) 1170−1174; (d) Y. Lin, Q. He, F. Zhao, L. Huo, J. Mai, X. Lu, C.-J. Su, T. Li, J. Wang, J. Zhu, Y. Sun, C. Wang, X. Zhan, J. Am. Chem. Soc. 138 (2016) 2973−2976; (e) Y. Yang, Z.-G. Zhang,
SC
H. Bin, S. Chen, L. Gao, L. Xue, C. Yang, Y. Li. J. Am. Chem. Soc. 138 (2016)
M AN U
15011−15018; (f) Y. Lin, F. Zhao, Q. He, L. Huo, Y. Wu, T.C. Parker, W. Ma, Y. Sun, C. Wang, D. Zhu, A.J. Heeger, S.R. Marder, X. Zhan, J. Am. Chem. Soc. 138 (2016) 4955−4961; (g) S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 29 (2016) 9423−9429.
TE D
[16] (a) H. Yao, Y. Chen, Y. Qin, R. Yu, Y. Cui, B. Yang, S. Li, K. Zhang, J. Hou, Adv. Mater. 28 (2016) 8283–8287; (b) Y. Qin, Y. Chen, Y. Cui, S. Zhang, H. Yao, J. Huang, W. Li, Z. Zheng, J. Hou, Adv. Mater. 29 (2017) 1606340; (c) W. Zhao, S. Li, H. Yao,
EP
S. Zhang, Y. Zhang, B. Yang, J. Hou, J. Am. Chem. Soc. 139 (2017) 7148−7151; (d) Y.
AC C
Cui, H. Yao, B. Gao, Y. Qin, S. Zhang, B. Yang, C. He, B. Xu, J. Hou, J. Am. Chem. Soc. 139 (2017) 7302−7309; (e) N. Qiu, H. Zhang, X. Wan, C. Li, X. Ke, H. Feng, B. Kan, H. Zhang, Q. Zhang, Y. Lu, Y. Chen, Adv. Mater. 29 (2017) 1604964; (f) B. Kan, H. Feng, X. Wan, F. Liu, X. Ke, Y. Wang, Y. Wang, H. Zhang, C. Li, J. Hou, Y. Chen, J. Am. Chem. Soc. 139 (2017) 4929−4934. [17] (a) J. Zhu, Z. Ke, Q. Zhang, J. Wang, S. Dai, Y. Wu, Y. Xu, Y. Lin, W. Ma, W. You, X. Zhan, Adv. Mater. 30 (2018) 1704713; (b) Y. Duan, X. Xu, H. Yan, W. Wu, Z. 25
ACCEPTED MANUSCRIPT Li, Q. Peng, Adv. Mater. 29 (2017) 1605115; (c) W. Jiang, R. Yu, Z. Liu, R. Peng, D. Mi, L. Hong, Q. Wei, J. Hou, Y. Kuang, Z. Ge, Adv. Mater. 30 (2018) 1703005; (d) J. Zhang, Y. Li, J. Huang, H. Hu, G. Zhang, T. Ma, P.C.Y. Chow, H. Ade, D. Pan, H. Yan,
RI PT
J. Am. Chem. Soc. 139 (2017) 16092–16095; (e) B. Kan, H. Feng, X. Wan, F. Liu, X. Ke, Y. Wang, Y. Wang, H. Zhang, C. Li, J. Hou, Y. Chen, J. Am. Chem. Soc. 139 (2017) 4929−4934; (f) H. Li, Z. Xiao, L. Ding and J. Wang, Sci. Bull. 63 (2018)
SC
340–342.
M AN U
[18] (a) J.E. Coughlin, Z.B. Henson, G.C. Welch, G. . Bazan, Acc. Chem. Res. 47 (2014) 257–270; (b) Y. Chen, X.J. Wan, G. Long, Acc. Chem. Res. 46 (2013) 2645–2655; (c) J.E. Coughlin, Z.B. Henson, G.C. Welch, G.C. Bazan, Acc. Chem. Res. 47 (2014) 257–270.
TE D
[19] (a) S. Zhang, L. Yang, D. Liu, C. He, J. Zhang, Y. Zhang, J. Hou, Sci. China Chem. 60 (2017) 1340–1348; (b) J.-L. Wang, K.-K. Liu, J. Yan, Z. Wu, F. Liu, F. Xiao,
7687–7697.
EP
Z.-F. Chang, H.-B. Wu, Y. Cao, T.P. Russell, J. Am. Chem. Soc. 138 (2016)
AC C
[20] K. Wang, B. Guo, Z. Xu, X. Guo, M. Zhang, Y. Li, ACS Appl. Mater. Interfaces 7 (2015) 24686−24693.
[21] (a) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang, J. Hou, Chem. Rev. 116 (2016) 7397–7457; (b) J. Hou, M.H. Park, S. Zhang, Y. Yao, L. Chen, J. Li, Y. Yang, Macromol. 41 (2008) 6012−6018; (c) L. Ye, S. Zhang, L. Huo, M. Zhang, J. Hou, Acc. Chem. Res. 47 (2014) 1595−1603. [22] (a) M. Zhang, X. Guo, W. Ma, S. Zhang, L. Huo, H. Ade, J. Hou, Adv. Mater. 26 (2014) 2089–2095; (b) M. Zhang, Y. Gu, X. Guo, F. Liu, S. Zhang, L. Huo, T.P. 26
ACCEPTED MANUSCRIPT Russell, J. Hou, Adv. Mater. 25 (2013) 4944–4949; (c) M. Zhang, X. Guo, W. Ma, H. Ade, J. Hou, Adv. Mater. 27 (2015) 4655–4660; (d) C. Cui, W.-Y. Wong, Y. Li, Energy Environ. Sci. 7 (2014) 2276. [23] (a) H. Son, W. Wang, T. Xu, Y. Liang, Y. Wu, G. Li, L. Yu, J. Am. Chem. Soc.
RI PT
133 (2011) 1885−1894; (b) M. Zhang, X. Guo, S. Zhang, J. Hou, Adv. Mater. 26 (2014) 1118−1123.
[24] (a) G.C. Welch, L.A. Perez, C.V. Hoven, Y. Zhang, X.-D. Dang, A. Sharenko,
SC
M. F. Toney, E.J. Kramer, T.-Q. Nguyen, G.C. Bazan, J. Mater. Chem. 21 (2011) 12700–12709; (b) Z.B. Henson, G.C. Welch, T. Poll, G.C. Bazan, J. Am. Chem. Soc.
M AN U
134 (2012) 3766−3779; (c) J. Wolf, M. Babics, K. Wang, Q. Saleem, R.-Z. Liang, M. R. Hansen, P.M. Beaujuge, Chem. Mater. 28 (2016) 2058–2066. [25] T.S. Poll, J.A. Love, T.-Q. Nguyen, G.C. Bazan, Adv. Mater. 24 (2012) 3646–3649.
TE D
[26] (a) Y. Sun, G.C. Welch, W.L. Leong, C.J. Takacs, G.C. Bazan, A.J. Heeger, Nat. Mater. 11 (2011) 44–48; (b) D. Qian, W. Ma, Z. Li, X. Guo, S. Zhang, L. Ye, H. Ade, Z. Tan, J. Hou, J. Am. Chem. Soc. 135 (2013) 8464−8467; (c) J. Zhou, Y. Zuo, X.
EP
Wan, G. Long, Q. Zhang, W. Ni, Y. Liu, Z. Li, G. He, C. Li, B. Kan, M. Li, Y. Chen,
AC C
J. Am. Chem. Soc. 135 (2013) 8484−8487; (d) S. Shen, P. Jiang, C. He, J. Zhang, P. Shen, Y. Zhang, Y. Yi, Z. Zhang, Z. Li, Y. Li, Chem. Mater. 25 (2013) 2274−2281. [27] (a) M. M. Mandoc, W. Veurman, L. J. A. Koster, B. Boer, P. W. M. Blom, Adv. Funct. Mater. 17 (2007) 2167–2173; (b) C. M. Proctor, J. A. Love, T.-Q. Nguyen, Adv. Mater. 26 (2014) 5957–5961. [28] (a) B. Guo, W. Li, X. Guo, X. Meng, W. Ma, M. Zhang, Y. Li, Adv. Mater. 29 (2017) 1702291; (b) H. Yao, L. Ye, J. Hou, B. Jang, G. Han, Y. Cui, G.M. Su, C. Wang, B. Gao, R. Yu, H. Zhang, Y. Yi, H.Y. Woo, H. Ade, J. Hou, Adv. Mater. 29 27
ACCEPTED MANUSCRIPT (2017) 1700254; (c) C. M. Proctor, M. Kuik, T.-Q. Nguyen, Prog. Polym. Sci. 38 (2013) 1941−1960; (d) C.Z. Li, C.Y. Chang, Y. Zang, H.X. Ju, C.C. Chueh, P.W. Liang, N. Cho, D.S. Ginger, A.K. Jen, Adv. Mater. 26 (2014) 6262−6267; (e) B. Qiu,
Zhang, Y. Li, Chem. Mater. 29 (2017) 7543–7553.
RI PT
L. Xue, Y. Yang, H. Bin, Y. Zhang, C. Zhang, M. Xiao, K. Park, W. Morrison, Z.-G.
[29] J.-L. Wu, F.-C. Chen, Y.-S. Hsiao, F.-C. Chien, P. Chen, C.-H. Kuo, M.H. Huang, C.-S. Hsu, ACS Nano 5 (2011) 959–967.
SC
[30] (a) Y.-J. Hwang, H. Li, B.A.E. Courtright, S. Subramaniyan, S.A. Jenekhe, Adv.
M AN U
Mater. 28 (2016) 124–131; (b) M. Lenes, M. Morana, C.J. Brabec, P.W.M. Blom, Adv. Funct. Mater. 19 (2009) 1106–1111; (c) P. Schilinsky, C. Waldauf, C.J. Brabec, Appl. Phys. Lett. 81 (2002) 3885.
[31] L.J.A. Koster, V.D. Mihailetchi, R. Ramaker, P.W.M. Blom, Appl. Phys. Lett. 86 (2005) 123509.
TE D
[32] K. Wang , X. Guo , B. Guo , W. Li , M. Zhang , Y. Li, Macromol. Rapid
AC C
EP
Commun. 37 (2016) 1066−1073.
28
ACCEPTED MANUSCRIPT
Highlights： ： 1. BDTDPTz with A-D-A structured was synthesized for the application in Solar Cells.
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2. The OSCs shows a PCE of 6.28% with a lower PC71BM content of 40%.
3. PC71BM content of 40% is one of the lowest acceptor content in the
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active layer.
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solution-processable OSCs.
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4. BDTDPTz could be promising high performance donor in
S1566-1199(18)30521-4
DOI:
10.1016/j.orgel.2018.10.006
Reference:
ORGELE 4922
To appear in:
Organic Electronics
Received Date: 30 July 2018 Revised Date:
7 September 2018
Accepted Date: 6 October 2018
Please cite this article as: K. Wang, Z. Xu, Y. Geng, H. Li, C. Lin, L. Mi, X. Guo, M. Zhang, Y. Li, Synthesis of organic molecule donors for efficient organic solar cells with low acceptor content, Organic Electronics (2018), doi: https://doi.org/10.1016/j.orgel.2018.10.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Graphic Abstract Synthesis of Organic Molecule Donor for Efficient Organic Solar Cells with Low Acceptor Content
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Kun Wang,*a Zhuo Xub, Yuan Geng,a Hui Li,a Chunlei Lin,a Liwei Mi,a Xia Guo,*b
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Maojie Zhang*b and Yongfang Lib
A new planar A-D-A structured organic molecule, BDTDPTz, was designed and
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synthesized for the application as donor material in organic solar cells (OSCs). The OSCs based on BDTDPTz:PC71BM with a weight ratio of 1.5:1 and 0.25%
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1-Phenylnaphthalene treatment exhibit higher power conversion efficiency (PCE) of 6.28%. The optimized PC71BM content of 40% is one of the lowest acceptor content in the active layer reported so far for the high photovoltaic performance OSCs, and BDTDPTz
could
be
solution-processable OSCs.
promising
high
performance
donor
materials
in
ACCEPTED MANUSCRIPT
Synthesis of Organic Molecule Donors for Efficient Organic Solar Cells with Low Acceptor Content Kun Wang,*a Zhuo Xub, Yuan Geng,a Hui Li,a Chunlei Lin,a Liwei Mi,a Xia Guo,*b
a
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Maojie Zhang*b and Yongfang Lib
School of of Materials and Chemical Engineering, Zhongyuan University of
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Technology, Zhengzhou 451191, China
b
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E-mail: [email protected]
Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical
Engineering and Materials Science, Soochow University, Suzhou 215123, China
Abstract:
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E-mail: [email protected], [email protected]
A new planar A-D-A structured organic small molecule semiconductor (O-SMS) with
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dialkyl-thiophene substituted benzodithiophene (BDT) as central electron-rich core
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flanked by relatively electron-deficient units of [1,2,5]thiadiazolo[3,4-c]pyridine (PTz) and terminated with alkyl-bithiophene as π-conjugated end-caps, BDTDPTz, was designed and synthesized for the application as donor material in organic solar cells (OSCs). BDTDPTz possesses wider absorption spectra with an optical bandgap of 1.65 eV, lower the highest occupied molecular orbital (HOMO) energy level of -5.42 eV and highly crystalline structures in solid films. The OSCs based on BDTDPTz:PC71BM blend film with a lower PC71BM content of 40% demonstrate a 1
ACCEPTED MANUSCRIPT power conversion efficiency (PCE) of 6.28% with a relatively higher open-circuit voltage of 0.868 V and short circuit current density of 12.83 mA cm–2. These results indicate that highly coplanar and crystalline structure of BDTDPTz can effectively
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reduce the content of fullerene acceptor in the active layer and then enhance the absorption and PCE of the OSCs.
Keywords: organic solar cells, organic small molecular donor materials,
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[1,2,5]thiadiazolo[3,4-c]pyridine, benzodithiophene, low acceptor content.
1. Introduction:
Solution-processable bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted broad interests due to their potential applications in next-generation
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lightweight and flexible solar cells, via low cost solution coating technologies and large area printing [1-5]. Active layer of the OSCs is composed of a p-type conjugated polymer [6-8] or organic small molecule [9-11] as donor blending with a fullerene
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derivative [12,13] or a nonfullerene n-type organic semiconductor [14-17] as acceptor.
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BHJ becomes a widely used system in the field of organic photovoltaic because it can form a bicontinuous interpenetrating network which composed by the electron donor and acceptor materials [1]. The bicontinuous interpenetrating network enhances the donor/acceptor interfacial area available for exciton dissociation and thus reduces the distance the exciton needs to travel before reaching an interface [2f]. For the acceptor, fullerene derivatives, such as [6,6]-phenyl-C61-butyric 2
ACCEPTED MANUSCRIPT acid-methylester, [6,6]-phenyl-C71-butyric acid-methyl-ester (PC71BM) and indene-C60 bisadduct ICBA are the most investigated acceptor due to their high electron affinity and excellent electron transport ability. On the other hand, for the donor, especially
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the organic small molecule (O-SM) containing a central electron-rich core flanked by relatively electron-poor units and terminated with π-conjugated end-caps, was regarded as one of the most successful organic small molecular semiconductor
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(O-SMS) frameworks due to the powerful photoelectric conversion efficiency (PCE)
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could be almost comparable to that of polymers [18,19].
In our previous work [20], we have synthesized a O-SMS donor material named as BDT-BTF for fullerene-based OSCs. BDT-BTF exhibits a slightly wider bandgap of 1.78 eV with the maximum absorption peaks (λmax) of 643 nm, a moderate highest
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occupied molecular orbital (HOMO) energy level of −5.20 eV, and a high hole mobility (µh) of 1.07×10−2 cm2 V−1 s−1. As a result, the BDT-BTF:PC71BM-based OSCs exhibit a satisfactory PCE of 5.88% with a low fullerene acceptor content of
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25%, an open-circuit voltage (Voc) of 0.85 V, a short circuit current density (Jsc) of
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10.48 mA cm−2, and a fill factor (FF) of 66%. Benzo[1,2-b:4,5-b’]dithiophene (BDT) was used as the central electron-rich core because it has a symmetric and planar conjugated structure and the compact stacking and coplanar molecule can be expected for the BDT-based materials. And the BDT unit has also proved to be one of the most famous building blocks for constructing both conjugated polymer and O-SMS materials in OSCs [21]. In addition, the absorption spectra, molecular energy levels and mobilities of the BDT-based organic semiconductors can be highly tuned by 3
ACCEPTED MANUSCRIPT modifying the functional substituents in the BDT unit [22,23]. For further enhancing the performance of this kind of materials, we selected [1,2,5]thiadiazolo[3,4-c]pyridine (PTz) unit with stronger electron-withdrawing
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ability as acceptor unit [24]. Furthermore, good film-forming characteristics is one of the essential properties of O-SMS, hence, we adopted dialkyl-thiophene side chain on BDT unit as the donor building block.
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To take the advantages of the synergistic strong electron-withdrawing ability of the
film-forming
organic
molecule
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backbone of PTz units and dialkyl-thiophene side chain on BDT unit, a good donor
material
namely
BDTDPTz
with
A-D-A-structure was synthesized and applied as donor material in OSCs. BDTDPTz film shows stronger and wider absorption, low-lying HOMO energy level, better
BDTDPTz:PC71BM
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film-forming and stronger crystallinity compared with BDT-BTF. The OSCs based on film
at
a
D:A weight
ratio
of
1.5:1
with
0.25%
1-Phenylnaphthalene (PN) treatment exhibit higher PCE of 6.28% with a high Voc of
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0.868 V, Jsc of 12.83 mA cm–2 and FF of 56.4%. The OSCs with 40% PC71BM content
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is one of the lowest optimized content of fullerene acceptor in OSCs reported so far. We also investigated the optimized photovoltaic performance of OSCs by the measurements of photoluminescence spectra, light intensity dependence of Jsc values and active layer morphology analysis. The results demonstrated that BDTDPTz could be promising high performance donor materials in solution-processable OSCs.
2. Experimental Section All chemicals and solvents were reagent grades and purchased from J&K, Aldrich and 4
ACCEPTED MANUSCRIPT Alfa Aesar. Monomers BDT and PTz were purchased from Solarmer Materials Inc. and SunaTech Inc., respectively. The detailed synthetic processes of the organic molecule and the detailed fabrication and characterization of the OSC devices were
C8H17
S
S
N
N
S SnMe3 + Br
Me3Sn S
S
S C8H17
C6H13
PTz
C8H17
BDT
C8H17
C8H17
S
N
C6H13
N
S
S
N
S
S
N
S
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S
Pd(PPh3)4 24 h
S
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N
Toluene 110 oC
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C8H17
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described in Supporting Information (SI).
N
S
C6H13
N
S C8H17
BDTDPTz
EP
C8H17
S
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Scheme 1. Synthesis route and molecular structure of BDTDPTz. 3. Results and Discussion The synthesis route and chemical structure of BDTDPTz are shown in Scheme 1. The molecular structure was confirmed by 1H Nuclear Magnetic Resonance (1H NMR) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS), as shown in Fig. S1 and Fig. S2 in SI. The acceptor of PC71BM is commercially available. The donor material BDTDPTz was prepared by stille 5
ACCEPTED MANUSCRIPT coupling reaction, and the detailed synthetic processes were described in SI. BDTDPTz exhibits excellent solubility in common organic solvents, such as chloroform, toluene, chlorobenzene, o-dichlorobenzene, etc. BDTDPTz shows broad
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and strong optical absorption in the wavelength range from 300 to 750 nm. Density functional theory (DFT) was employed to gain further insight into the molecular coplanarity and calculate the frontier molecular orbitals surfaces (HOMO and Lowest
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Unoccupied Molecular Orbital (LUMO)) of the optimal geometries for BDTDPTz at
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the B3LYP/6-31G (d, p) level, as shown in Fig. S3 in SI. The calculated HOMO and LUMO energy levels of BDTDPTz are −4.81 eV and −3.03 eV, respectively. The molecular orbital distributions as shown in Fig. S3 (a) and (b) indicate that the HOMO of BDTDPTz was delocalized along the whole π-conjugated backbone of the
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molecule while its LUMO is mainly localized on the PTz-based acceptor segment of BDTDPTz and partially extend along the skeleton of the BDT units. The dihedral angles between the BDT unit and the thiophene unit in side chain is 54.57 º(Fig.
EP
S3(c)). BDTDPTz shows a linear coplanar molecular skeleton conformation from the
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sideview (Fig. S3(d)), which is beneficial for intermolecular π-π stacking.
Normalized Absorption (a.u.)
3.1 UV-Vis Absorption Spectra and Electronic Energy Levels
1.4 1.2
in solution in film
(b)
(a)
1.0 0.8 0.6 0.4 0.2 0.0 300
400
500 600 700 Wavelength (nm)
800
-1.5
6
-1.0 -0.5 0.0 0.5 1.0 + Potential (V vs Ag/Ag )
1.5
ACCEPTED MANUSCRIPT Fig. 1. (a) UV-Vis absorption spectra of BDTDPTz in chloroform solution and solid films; (b) cyclic voltammograms of BDTDPTz film on the glassy carbon electrode in 0.1 mol L−1 Bu4NPF6 in acetonitrile solution at a scan rate of 50 mV s−1. UV-Vis absorption spectra of the solutions in chloroform and the solid thin film of
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BDTDPTz were shown in Fig. 1 (a). BDTDPTz exhibits λmax at 597 nm in chloroform solution with a shoulder peak at 533 nm. From solution to solid state thin film, the absorption spectra of BDTDPTz shows distinctly red-shifts, with a
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concomitant more intense peak at 683 nm, implying that BDTDPTz should have
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strong intermolecular π-π interaction in solid state. The absorption edge (λedge) of BDTDPTz film is at 750 nm, corresponding to an optical bandgap of 1.65 eV. It's worth noting that either λmax or λedge of BDTDPTz (both in solution and solid film) had a red-shifted absorption than its analogue BDT-BTF we reported before [20], the
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correlation data were collected in Table 1. The broad absorption of BDTDPTz is beneficial for achieving a higher Jsc in the OSCs devices. The absorption profile of
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BDTDPTz:PC71BM blend films are presented in Fig. S4 in SI. The HOMO and LUMO levels of BDTDPTz were determined by the cyclic
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voltammogram (CV) measurement as shown in Fig. 1(b). The CV results indicate that the HOMO and LUMO energy levels of BDTDPTz are −5.42 eV and −3.65 eV, respectively. Both the HOMO and LUMO energy levels of BDTDPTz has down-shifted compared with the donor material of BDT-BTF, the correlation data were collected in Table 1. These data suggest that BDTDPTz was appropriate for the application as donor materials with PC71BM acceptor in photovoltaic devices. What is more, the deep HOMO energy level of BDTDPTz is beneficial for achieving a higher 7
ACCEPTED MANUSCRIPT Voc in the OSCs devices based on BDTDPTz as donor material. The relevant optical and electrochemical parameters were collected in Table 1 for a clear comparison. Table 1 Optical, electrochemical and thermochemistry properties of BDTDPTz Td (°C)
a
Material
Tm (°C)
Tx (°C)
λmax (nm) Sol.
λmax (nm) film
BDTDPTz
433
213
199
597
683
1.65
-5.42
-3.65
BDT-BTF
425
213
196
559
643
1.78
-5.20
-3.4220
Egopt (eV)
d
HOMO (eV)
e
LUMO (eV)
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c
Tm = endothermic peak; bTx = exothermic peak; cEgopt=1240/λedge; dHOMO = -e (φox +
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4.71) (eV); eLUMO = -e (φred + 4.71) (eV).
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a
b
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3.2 Optical-to-Electrical Conversion Process
Fig. 2. Molecular energy level diagrams of BDTDPTz and PC71BM.
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The process of optical-to-electrical conversion process in the blend film can be summarized in a series of sequential steps as follows: 1) Absorption of a photon generates the exciton; 2) Exciton diffusion to the donor/acceptor interfaces; 3) Charge transfer i.e. exciton disscociation into a free electron and hole pair; 4) Charge collection at the corresponding electrode [1b]. The molecular energy levels of the active layer materials play an important role in optical-to-electrical conversion process. As shown in Fig. 2, the molecular energy levels of BDTDPTz and PC71BM 8
ACCEPTED MANUSCRIPT displayed a larger ∆EHOMO (EHOMOdonor−EHOMOacceptor) of 0.45 eV, which would facilitate to obtain a higher Jsc in devices. The ∆ELUMO (ELUMOdonor−ELUMOacceptor) in BDTDPTz:PC71BM pair is 0.26 eV, which provides a powerful driving force for the
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charge separation at the bulk interface. Furthermore, the lower HOMO energy levels of BDTDPTz are beneficial to a higher Voc for the OSCs with the BDTDPTz as donor because Voc of OSCs is related to the difference of the LUMO of the acceptor
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and the HOMO of the donor materials. In addition, the strong crystallinity of
recombination in devices.
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BDTDPTz is beneficial to form favorable blend morphology and hence to suppress
3.3 Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) analysis
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Thermogravimetric analysis (TGA) was used to evaluate the thermal stability of BDTDPTz (Fig. 3(a)), the decomposition temperature (Td) (at 5% weight loss) of
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BDTDPTz was approximately 433 °C. The high Td indicates that BDTDPTz has excellent thermal stability in organic optoelectronic devices. The thermodynamic
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properties were analyzed by differential scanning calorimetry (DSC) measurement and the thermograms were obtained from -20 to 300 °C (Fig. 3(b)). BDTDPTz shows an apparent endothermic peak at 213 °C and a clear exothermic peak at 196 °C. According to the DSC analysis, we can find that BDTDPTz molecules have strong crystallizing ability. The relevant thermochemistry parameters were collected in Table 1.
9
ACCEPTED MANUSCRIPT 5 (a)
4
Weight (%)
−1
433 ºC
80 60 40
BDTDPTz
100
200 300 400 500 Temperature (ºC)
(b)
3 2 Cool
1 0 Heat
-1 -2 -3 -50
600
199 ºC
213 ºC
0
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Heat Flow (W g )
100
50 100 150 200 250 300 Temperature (ºC)
Fig. 3. (a) TGA plots of BDTDPTz with a heating rate of 10 °C min˗1 under the
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nitrogen atmosphere; (b) DSC thermogram of BDTDPTz with a scan rate of 5 °C min˗1 under nitrogen atmosphere.
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3.4 Photovoltaic Properties of the OSCs
We optimized the device fabrication process with a structure of indium tin oxide (ITO)/poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) (20 (7
nm)/BDTDPTz:PC71BM/
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nm)/MoO3
poly[(9,9-bis(3′-(N,N-dimethyl)-nethylammoinium-propyl)-2,7-fluorene)-alt-2,7-(9,9dioctylfluorene)]dibromide (PFN-Br)/Al(100 nm). It is noteworthy that, we choose
EP
MoO3 as a thin interlayer between PEDOT:PSS and active layer, mainly because of
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the acidic nature of the PEDOT:PSS, which ultimately results in protonation of the PTz pyridyl nitrogen [25]. Chloroform was applied to prepare the solution for spin-coating the active layer, and to further improve the photovoltaic performance, PN was adopted as the solvent additive. Fig. 4 shows the current density-voltage (J−V) curves of the devices with different donor/acceptor (D/A) weight ratios from 1:1 to 2.5:1 under 100 mW cm–2 AM 1.5G illumination, and Table 2 lists the photovoltaic parameters of the OSCs for a clear comparison.
10
(b) 50
1:1 1.5:1 2:1 2.5:1
-3
40
-6 -9 -12
30 1:1 1.5:1 2:1 2.5:1
20 10
-15 -0.2
0.0
0.2
0.4
0.6
0.8
0
1.0
400
(d)
(c)
60 without 0.25% PN 0.5% PN
50 EQE (%)
-3 -6 -9 -12 -15 -0.2
40
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−2
Current density (mA cm )
70 0
500
600
700
800
Wavelength (nm)
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Voltage (V)
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0
60
(a)
EQE (%)
−2
Current density (mA cm )
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Without 0.25% PN
30 20 10
0
0.0
0.2
0.4
0.6
0.8
Voltage (V)
1.0
400
500 600 700 Wavelength (nm)
800
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Fig. 4. (a) J–V curves and (b) the corresponding EQE curves of the devices based on BDTDPTz:PC71BM blend film with different D/A ratios; (c) J–V curves and (d) the corresponding EQE curves of the devices based on BDTDPTz:PC71BM (D/A = 1.5:1)
EP
active layer with additive of PN.
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The OSCs devices based on BDTDPTz:PC71BM blend film with a D/A ratio of 1:1 (where the content of PC71BM is 50%) exhibits a PCE of 4.11%, accompanying with a Voc of 0.870 V, Jsc of 9.04 mA cm–2, and a FF of 52.3%. When the D/A weight ratio of the blend film increased to 1.5:1, where the PC71BM content decreased to 40%, a higher PCE of 4.98% was obtained, which benefitted from the enhanced Jsc and slightly improved Voc. Further decreasing the content of PC71BM acceptor, the PCE declined to 3.93% for the OSCs with D/A ratio of 2:1 where the PC71BM content is
11
ACCEPTED MANUSCRIPT 33% and 3.15% for the OSCs with D/A ratio of 2.5:1 where the PC71BM content is 28%, respectively, although the OSCs exhibit an almost constant Voc of 0.865–0.874 V. The declined PCE values of the devices were mainly due to the decreased Jsc and
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FF (as shown in Fig. 4(c) and Table 2). The OSCs with the D/A weight ratio of 1.5:1 for our new donor material PBDTBTz-T is one of the lowest optimized content of fullerene acceptor (40%) in OSCs reported in literature so far [26].
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The external quantum efficiency (EQE) spectra of the above-mentioned devices are
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shown in Fig. 4(b). The EQE curves of these devices with different D/A ratio cover a wavelength range from 350-750 nm, which agrees with the absorption spectra of the active layer. When the PC71BM content is 40%, the OSCs displayed a maximum EQE response value of 53.7% at 560 nm.
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Table 2 Photovoltaic parameters of the OSCs based on BDTDPTz:PC71BM with different conditions under the illumination of AM 1.5G, 100 mW cm–2. Voc (V)
Jsc/Jsca (mA cm–2)
FF (%)
PCE (%)
0.870
9.04/8.72
52.3
4.11
0.874
10.96/10.53
51.9
4.98
0.871
9.55/9.06
47.3
3.93
2.5:1
0.865
8.64/8.26
42.1
3.15
1.5:1 (0.25% PN)
0.868
12.83/12.31
56.4
6.28
1.5:1 (0.5% PN)
0.878
10.20
49.0
4.38
1:1 1.5:1
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2:1
EP
D/A ratio
a
Integrated from EQE In order to further improving the photovoltaic performance of OSCs devices, on the
basis of D/A weight ratio of 1.5:1, we examined the role of additives, PN finally was 12
ACCEPTED MANUSCRIPT selected as solvent additive (as shown in Fig. 4(c)). As reported in the literature25, 26a, we are very carefully to adjust the amount of the additive. An optimized PCE of the device reached 6.28% with a Voc of 0.868 V, Jsc of 12.83 mA cm–2, and a FF of 56.4%
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when the additive PN content is 0.25%. The corresponding EQE curves displayed a wide response range in the wavelength region of 350–750 nm with a maximum value of 64.4%, indicating efficient photoelectron conversion in the device. Increasing the
SC
PN content leads to deterioration in performance. The corresponding UV-Vis spectra
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are shown in Fig. S4 in SI.
The current density values calculated from the EQE curves are consistent with those obtained from the J–V measurement with deviation less than 5% (see Table 2), indicating that the J−V measurements in this work are reliable.
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In addition to efficiency, device stability is another important factor influencing the OSCs commercial application. High device stability is a necessary prerequisite for practical applications of OSCs. Here, we tested
EP
the storage stability of the device. However, the result was not
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satisfactory, the PCE of the OSCs dropped to 80 percent of its original value after 48 h of storage in the N2-filled glove box (Figure S6). We thought that the decreased efficiency was mainly caused by the instability of device structure and active layer morphology. 3.5 Photoluminescence Quenching Effect
13
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84.6% 90.8% 800 900 1000 1100 1200 Wavelength (nm)
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@695 nm BDTDPTz D/A=1.5:1 D/A=1.5:1 with 0.25% PN
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Fig. 5. Photoluminescence spectra of BDTDPTz and BDTDPTz:PC71BM blend films (D/A = 1.5:1) with or without PN.
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Photoluminescence (PL) quenching experiment was used to investigate the photoinduced exciton dissociation and charge transfer efficiency in the blend films. According to the maximum absorptions, excitation wavelengths in the PL measurements were selected to be 695 nm. As shown in Fig. 5, the
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BDTDPTz:PC71BM blend film with additive treatment demonstrated more than 90% PL quenching compared to the PL spectra of the pure BDTDPTz, the value is higher
EP
than those of the blends without solvent additive treatment. Higher PL quenching efficiency means that the BDTDPTz:PC71BM blend film with solvent additive
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treatment have an effective photoinduced exciton dissociation and charge transport, which is in agreement with the higher EQE and PCE values of the corresponding OSCs device.
3.6 Carier Mobility In order to better understand the effect of solvent additive on the photovoltaic performance of the OSCs devices, both the hole (with a hole-only device structure, 14
ACCEPTED MANUSCRIPT ITO/PEDOT:PSS/MoO3/Active layer/MoO3/Al) and electron (with an electron-only device structure, ITO/ZnO(gel)/Active layer/ZnO(NPS)/Al) mobilities (µh and µe) of BDTDPTz and BDTDPTz:PC71BM blend films were measured by the space charge
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limited current (SCLC) method as shown in Fig. S5 in SI, and the corresponding data are collected in Table S1 in SI. The µh of the pure BDTDPTz is 2.38×10−4 cm2 V−1 s−1, but the µe of BDTDPTz is too low to be measured. The µh and µe of
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BDTDPTz:PC71BM (with D/A ratio of 1.5:1) blend film are calculated to be 3.44×
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10-5 cm2 V−1 s−1 and 3.29×10-4 cm2 V−1 s−1, respectively, with µe/µh ratio of 9.56. After solvent additive treatment, the µh and µe values of the device were increased to 8.20×10-5 cm2 V−1 s−1 and 3.73×10-4 cm2 V−1 s−1, respectively, with µe/µh ratio of 4.55. Here, we noticed that the unbalance hole and electron mobilities (i.e. µe/µh ratio)
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of the blend film were further expanded compared to BDT-BTF [20], on the other hand, both the hole and electron mobility of the active layer have decreased to a certain extent (<10-4 cm2 V−1 s−1) compared to BDT-BTF [27], thus, a lower FF was
EP
observed in the OSCs. We thought this could be caused by the addition of alkyl side
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chains on the BDT unit.
3.7 Light Intensity Dependence
15
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(a) Without 0.25% PN
−2
Jph (mA cm− )
10
0.1 0.01
0.1
1
0.88 (b)
(c) 0.86
10
0.84
without (S=0.928) 0.25% PN (S=0.957)
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Voc (V)
−2
Jph (mA cm− )
SC
Veff (V)
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1
0.82 0.8
without (1.52 kT /q) 0.25% PN (1.28 kT /q)
0.78
1 10
100 −2 Light intensity (mW cm )
10
−2
100
Light intensity (mW cm )
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Fig. 6. (a) Jph versus Veff characteristics, and dependence of Jph (b) and Voc (c) on light intensity for the OSCs based on BDTDPTz:PC71BM (1.5:1, w/w) with/without solvent additive treatment.
EP
For further understanding the influence of the solvent additive on the exciton
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dissociation and charge collection process of the OSCs, the dependence of the photocurrent (Jph) on the effective voltage (Veff) were measured and analyzed according to our or other group’s reported work [19a,28], as shown in Fig. 6(a). The calculated exciton dissociation probability (Pdiss) under short-circuit conditions is determined by the normalized Jph at the saturated current density (Jsat), i.e. Jph/Jsat ratio [29]. The Pdiss values of BDTDPTz:PC71BM devices (D/A = 1.5:1) without or with PN additive were calculated as 74.2% and 80.8%, respectively, indicating exciton
16
ACCEPTED MANUSCRIPT dissociation and charge collection in the latter device is more efficient than that in the former. The dependence of photocurrent (Jph) and Voc under different light intensities offers
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deeper insight into the influence of additive treatment on recombination process in the OSCs device, as shown in Fig. 6(b). The relationship of Jph and the light intensity (Plight) can be expressed as Jph∝PlightS, where the exponential factor S implies the
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extent of the bimolecular recombination. A linear dependence of Jph on Plight with S
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value close to 1 implies weak bimolecular recombination in the device [30]. For both of the devices without or with PN treatment, the S values were 0.928 and 0.957, respectively, indicating that additive treatment can effectively reduce the occurrence of bimolecular recombination process in BDTDPTz:PC71BM film with D/A ratio of
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1.5:1.
The slope of Voc versus lnPlight can helps us to estimate the degree of trap-assisted recombination in the devices, as shown in Fig. 6(c). The relationship between Voc and
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Plight could be described as Voc∝lnPlight, and the slope of the fitting straight line should
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be kT/q (where q is the elementary charge, k is the Boltzmann constant, and T is the Kelvin temperature) if bimolecular recombination is the exclusive recombination form [31]. In our cases, the device with additive treatment showed a slope of 1.28 kT/q, smaller than the device without PN with a slope of 1.52 kT/q. This result indicates that additive treatment could suppress trap-assisted recombination in the active layer, leading to an improved Jsc. 3.8 Morphology Studies of the Active Layer 17
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Fig. 7. AFM height (a, d) and phase (b, e) images of the blend films of
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BDTDPTz:PC71BM (1.5:1, w/w) without/with solvent additive; TEM images of BDTDPTz:PC71BM (1.5:1, w/w) without (c)/with (f) solvent additive. For further explaining the effect of solvent additive on the photovoltaic
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performance of the OSCs based on BDTDPTz:PC71BM blend film with D/A ratio of 1.5:1, we measured the morphology of the active layers by atomic force microscopy
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(AFM) and transmission electron microscopy (TEM). As shown in Fig. 7, the BDTDPTz:PC71BM film without solvent additive (Fig. 7(a)) has higher surface roughness (Rq) than the blend film with 0.25% PN (Fig. 7(d)), i.e. 3.41 nm versus 1.45 nm, and also the larger granular aggregations can be observed in the former (Fig. 7(b)), implying that the former film has stronger phase separation than the latter (Fig. 7(e)). Large-scale phase-separated morphology (>50 nm) can be clearly seen in the TEM image (Fig. 7(c)), which may cause more geminate recombination and 18
ACCEPTED MANUSCRIPT bimolecular recombination, and thus results in lower Jsc of the OSCs device. Accompanied with solvent additive treatment, the size of the granular aggregates reduced gradually. An appropriate D/A interpenetrating network was observed with
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size of ca. 10~20 nm for the BDTDPTz and PC71BM networks by 0.25% PN treatment (Fig. 7(f)), which indicates that BDTDPTz have a good miscibility with PC71BM in the active layers. The AFM morphologies correlate well with the images
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observed from TEM. The interpenetrating network of the blend films indicates that
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the organic molecules with the molecular structure like BDTDPTz could be forming efficient percolation channels in solution-processable OSCs [20, 26a, 32]. The efficient percolation channels is beneficial for charge separation and transport, thus improving the carrier collection efficiency and leading to a high Jsc, which agrees well
4. Conclusions
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with the optimized photovoltaic performance of the OSCs.
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In conclusion, a new organic molecule with BDT as central donor unit and PTz as acceptor unit, BDTDPTz, was rationally designed and synthesized for the application
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as donor material in OSCs. Compared with BDT-BTF molecule, BDTDPTz with dialkyl side chains on BDT unit and nitrogen-atoms substitution on BT unit exhibits stronger and broader absorption, lower-lying HOMO energy level, good film-forming and stronger crystallinity. The OSCs based on BDTDPTz:PC71BM film at a D:A weight ratio of 1.5:1 with 0.25% PN treatment exhibit higher PCE of 6.28% with a higher Voc of 0.868 V, Jsc of 12.83 mA cm–2 and FF of 56.4% . The OSCs with 40% PC71BM content is one of the lowest optimized content of fullerene acceptor in OSCs 19
ACCEPTED MANUSCRIPT reported so far. The improvement of the photovoltaic performance by additive treatment was studied by the measurements of photoluminescence spectra, light intensity dependence of Jsc values and active layer morphology analysis. Our results
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confirm that the OSCs based on BDTDPTz:PC71BM film with additive treatment possess higher charge separation and transportation efficiency, less charge recombination and good donor/acceptor nanoscale phase separated interpenetrating
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network and, therefore, demonstrated higher photovoltaic performance. However, the
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overall performance of the OSCs device was limited by the lower charge carrier mobility of BDTDPTz. In considering the simple molecular structures of BDTDPTz and the satisfactory photovoltaic performance, as well as the photophysical properties, the A-D-A-type donor materials can be further tuned through molecular engineering
BDTDPTz
could
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on the A or D units, thus, the organic molecules with the molecular structure like be
promising
high
performance
donor
materials
in
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solution-processable OSCs.
ACKNOWLEDGEMENTS
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This work was supported by the National Natural Science Foundation of China (21502134, 51573120 and 51773142), Henan Province Science and Technology Planning Project (182102210530), Zhongyuan University of Technology Youth Backbone Teachers Funding Planning Project and Program for Interdisciplinary Direction Team in Zhongyuan University of Technology, China.
References: 20
ACCEPTED MANUSCRIPT [1] (a) G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789–1791; (b) S. R. Forrest, MRS Bull. 30 (2005) 28-32. [2] (a) S. Günes, H. Neugebauer, N.S. Sariciftci, Chem. Rev. 107 (2007) 1324–1338; 488 (2012)
RI PT
(b) M. Graetzel, R.A. J. Janssen, D.B. Mitzi, E.H. Sargent, Nature
304–312; (c) X. Guo, M. Baumgarten, K. Müllen, Prog. Polym. Sci. 38 (2013) 1832–1908; (d) K.A. Mazzio, C.K. Luscombe, Chem. Soc. Rev. 44 (2015) 78–90; (e)
SC
X. Che, Y. Li, Y. Qu, S.R. Forrest, Nat. Energy, 3 (2018) 422–427; (f) T. M. Clarke,
M AN U
J. R. Durrant, Chem. Rev. 110 (2010) 6736–6767.
[3] (a) Z. He, H. Wu, Y. Cao, Adv. Mater. 26 (2014) 1006–1024; (b) Y.F. Li, Acc. Chem. Res. 45 (2012) 723; (c) Z.-G. Zhang, Y.F. Li, Sci. China Chem. 58 (2015) 192–209.
TE D
[4] (a) L. Lu, T. Zheng, Q, Wu, A.M. Schneider, D. Zhao, L. Yu, Chem. Rev. 115 (2015) 12666–12731; (b) G. Li, W.-H. Chang, Y. Yang, Nat. Rev. Mater. 2 (2017) 17043.
EP
[5] (a) F.C. Krebs, Sol. Energy Mat. Sol. C. 93 (2009) 394–412; (b) N. Espinosa, M.
AC C
Hösel, M. Jørgensen, F.C. Krebs, Energy Environ. Sci. 7 (2014) 855–866; (c) T.R. Andersen, H.F. Dam, M. Hösel, M. Helgesen, J.E. Carlé, T.T. Larsen-Olsen, S.A. Gevorgyan, J.W. Andreasen, J. Adams, N. Li, F. Machui, G.D. Spyropoulos, T. Ameri, N. Lemaître, M. Legros, A. Scheel, D. Gaiser, K. Kreul, S. Berny, O.R. Lozman, S. Nordman, M. Välimäki, M. Vilkman, R.R. Søndergaard, M. Jørgensen, C.J. Brabec, F.C. Krebs, Energy Environ. Sci. 7 (2014) 2925–2933. [6] (a) S.-H. Liao, H.-J. Jhuo, Y.-S. Cheng, S.-A. Chen, Adv. Mater. 25 (2013) 21
ACCEPTED MANUSCRIPT 4766–4771; (b) T.M. Swager, Macromol. 50 (2017) 4867–4886; (c) C. Liu, K. Wang, X. Gong, A.J. Heeger, Chem. Soc. Rev. 45 (2016) 4825–4846; (d) C.H. Cui, W.-Y. Wong, Y.F. Li, Energy Environ. Sci. 7 (2014) 2276–2284; (e) C.H. Cui, Z.C. He, Y.
RI PT
Wu, X. Cheng, H. Wu, Y. Li, Y. Cao, W.-Y. Wong, Energy Environ. Sci. 9 (2016) 885–891; (f) H. Hu, P.C.Y. Chow, G. Zhang, T. Ma, J. Liu, G. Yang, H. Yan, Acc. Chem. Res. 50 (2017) 2519−2528; (g) H. Bin, Z.-G. Zhang, L. Gao, S. Chen, L.
SC
Zhong, L. Xue, C. Yang, Y. Li, J. Am. Chem. Soc. 138 (2016) 4657–4664; (h) M.
M AN U
Zhang, X. Guo, W. Ma, H. Ade, J. Hou, Adv. Mater. 26 (2014) 5880–5885; (i) S. Li, L. Ye, W. Zhao, H. Yan, B. Yang, D. Liu, W. Li, H. Ade, J. Hou, J. Am. Chem. Soc. 140 (2018) 7159–7167.
[7] (a) B. Fan, L. Ying, P. Zhu, F. Pan, F. Liu, J. Chen, F. Huang, Y. Cao, Adv. Mater.
TE D
29 (2017) 1703906; (b) Z.-G. Zhang, Y. Yang, J. Yao, L. Xue, S. Chen, X. Li, W. Morrison, C. Yang, Y. Li, Angew. Chem. Int. Ed. 56 (2017) 13503–13507; (c) I. Osaka, K. Takimiya, Adv. Mater. 29 (2017) 1605218; (d) D. Liu, B. Yang, B. Jang, B.
EP
Xu, S. Zhang, C. He, H.Y. Woo, J. Hou, Energy Environ. Sci. 10 (2017) 546–551; (e)
AC C
W. Zhao, S. Li, H. Yao, S. Zhang, Y. Zhang, B. Yang, J. Hou, J. Am. Chem. Soc. 139 (2017) 7148−7151; (f) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang, J. Hou, Chem. Rev. 116 (2016) 7397–7457; (g) Y. Cui, H. Yao, C. Yang, S. Zhang, J. Hou, Acta Polym. Sin. 2 (2018) 223–230; (h) C. Sun, F. Pan, H. Bin, J. Zhang, L. Xue, B. Qiu, Z. Wei, Z.-G. Zhang, Y. Li, Nat. Commun. 9 (2018) 743. [8] (a) Z. He, B. Xiao, F. Liu, H. Wu, Y. Yang, S. Xiao, C. Wang, T.P. Russell, Y. Cao, Nat. Photonics
9 (2015) 174; (b) S. Nam, J. Seo, S. Woo, W.H. Kim, H. Kim, D.D.C. 22
ACCEPTED MANUSCRIPT Bradley, Y. Kim, Nat. Commun. 6 (2015) 8929; (c) N. Zhou, X. Guo, R.P. Ortiz, T. Harschneck, E.F. Manley, S.J. Lou, P.E. Hartnett, X. Yu, N.E. Horwitz, P.M. Burrezo, T.J. Aldrich, J.T.L. Navarrete, M.R. Wasielewski, L.X. Chen, R.P.H. Chang, A.
RI PT
Facchetti, T.J. Marks, J. Am. Chem. Soc. 137 (2015) 12565–12579; (d) K. Kawashima, Y. Tamai, H. Ohkita, I. Osaka, K. Takimiya, Nat. Commun. 6 (2015) 10085; (e) L. Lu, M.A. Kelly, W. You, L. Yu, Nat. Photonics
9 (2015) 491; (f) T. Liu,
SC
X. Pan, X. Meng, Y. Liu, D. Wei, W. Ma, L. Huo, X. Sun, T. H. Lee, M. Huang, H.
M AN U
Choi, J.Y. Kim, W.C.H. Choy, Y. Sun, Adv. Mater. 29 (2017) 1604251; (g) X. Xu, T. Yu, Z. Bi, W. Ma, Y. Li, Q. Peng, Adv. Mater. 30 (2018) 1703973. [9] (a) N. Qiu, H. Zhang, X. Wan, C. Li, X. Ke, H. Feng, B. Kan, H. Zhang, Q. Zhang, Y. Lu, Y. Chen, Adv. Mater. 29 (2017) 1604964; (b) H. Bin, Y. Yang, Z.-G. Zhang, L.
TE D
Ye, M. Ghasemi, S. Chen, Y. Zhang, C. Zhang, C. Sun, L.-W. Xue, C. Yang, H. Ade, Y. Li, J. Am. Chem. Soc. 139 (2017) 5085–5094; (c) Y. Lin, Y. Li, X. Zhan, Chem. Soc. Rev. 41 (2012) 4245–4272; (d) B. Walker, C. Kim and T.-Q. Nguyen, Chem. Mater.
EP
23 (2011) 470–482; (e) A. Mishra, P. Bäuerle, Angew. Chem. Int. Ed. 51 (2012)
AC C
2020–2067; (f) K. Sun, Z. Xiao, S. Lu, W. Zajaczkowski, W. Pisula, E. Hanssen, J.M. White, R.M. Williamson, J. Subbiah, J.Y. Ouyang, A.B. Holmes, W.W.H. Wong, D.J. Jones, Nat. Commun. 6 (2015) 6013. [10] (a) B. Kan, Q. Zhang, M. Li, X. Wan, W. Ni, G. Long, Y. Wang, X. Yang, H. Feng, Y. Chen, J. Am. Chem. Soc. 136 (2014) 15529–15532; (b) T. Li, T. Meyer, Z. Ma, J. Benduhn, C. Körner, O. Zeika, K. Vandewal, K. Leo, J. Am. Chem. Soc. 139 (2017) 13636−13639; 23
ACCEPTED MANUSCRIPT [11] (a) Q. Zhang, B. Kan, F. Liu, G. Long, X. Wan, X. Chen, Y. Zuo, W. Ni, H. Zhang, M. Li, Z. Hu, F. Huang, Y. Cao, Z. Liang, M. Zhang, T.P. Russell, Y. Chen, Nat. Photonics
9 (2014) 35–41; (b) B. Kan, M. Li, Q. Zhang, F. Liu, X. Wan, Y. Wang, W.
RI PT
Ni, G. Long, X. Yang, H. Feng, Y. Zuo, M. Zhang, F. Huang, Y. Cao, T.P. Russell, Y. Chen, J. Am. Chem. Soc. 137 (2015) 3886–3893.
[12] (a) Y.-Y. Lai, Y.-J. Cheng, C.-S. Hsu, Energy Environ. Sci. 7 (2014) 1866–1883;
SC
(b) S, Kirner, M. Sekita, D.M. Guldi, Adv. Mater. 26 (2014) 1482–1493; (c) S.-H.
M AN U
Liao, H.-J. Jhuo, Y.-S. Cheng, V. Gupta, S.-A. Chen, J. Mater. Chem. A 3 (2015) 22599–22604; (d) Z. Xiao, X. Geng, D. He, X. Jia, L. Ding, Energy Environ. Sci., 9 (2016) 2114–2121.
[13] (a) C. Cui, Y.W. Li, Y. Li, Adv. Energy Mater. 7 (2016) 1601251; (b) Y. Li, Chem.
TE D
Asian J. 8 (2013) 2316–2328; (c) Y. He, H.-Y. Chen, J. Hou, Y. Li, J. Am. Chem. Soc. 132 (2010) 1377–1382; (d) Y. He, G. Zhao, B. Peng, Y. Li, Adv. Funct. Mater. 20 (2010) 3383–3389; (e) X. Meng, G. Zhao, Q. Xu, Z. Tan, Z. Zhang, L. Jiang, C. Shu,
EP
C. Wang, Y. Li, Adv. Funct. Mater. 24 (2014) 158–163.
AC C
[14] (a) W. Jiang, Y. Li, Z. Wang, Acc. Chem. Res. 47 (2014) 3135−3147; (b) F. Würthner, C.R. Saha–Möller, B. Fimmel, S. Ogi, P. Leowanawat, D. Schmidt, Chem. Rev. 116 (2016) 962–1052; (c) Y. Zhong, M.T. Trinh, R. Chen, G.E. Purdum, P.P. Khlyabich, M. Sezen, S. Oh, H. Zhu, B. Fowler, B. Zhang, W. Wang, C.-Y. Nam, M.Y. Sfeir, C.T. Black, M.L. Steigerwald, Y.-L. Loo, F. Ng, X.-Y. Zhu, C. Nuckolls, Nat. Commun. 6 (2015) 8242; (d) J. Zhang, Y. Li, J. Huang, H. Hu, G. Zhang, T. Ma, P.C. Y. Chow, H. Ade, D. Pan, H. Yan, J. Am. Chem. Soc. 139 (2017) 16092–16095. 24
ACCEPTED MANUSCRIPT [15] (a) C. Yan, S. Barlow, Z. Wang, H. Yan, A.K.-Y. Jen, S.R. Marder, X. Zhan, Nat. Rev. Mater. 3 (2018) 18003; (b) Y. Lin, Z.-G. Zhang, H. Bai, J. Wang, Y. Yao, Y. Li, D. Zhu, X. Zhan, Energy Environ. Sci. 8 (2015) 610−616; (c) Y. Lin, J. Wang, Z.-G.
RI PT
Zhang, H. Bai, Y. Li, D. Zhu, X. Zhan, Adv. Mater. 27 (2015) 1170−1174; (d) Y. Lin, Q. He, F. Zhao, L. Huo, J. Mai, X. Lu, C.-J. Su, T. Li, J. Wang, J. Zhu, Y. Sun, C. Wang, X. Zhan, J. Am. Chem. Soc. 138 (2016) 2973−2976; (e) Y. Yang, Z.-G. Zhang,
SC
H. Bin, S. Chen, L. Gao, L. Xue, C. Yang, Y. Li. J. Am. Chem. Soc. 138 (2016)
M AN U
15011−15018; (f) Y. Lin, F. Zhao, Q. He, L. Huo, Y. Wu, T.C. Parker, W. Ma, Y. Sun, C. Wang, D. Zhu, A.J. Heeger, S.R. Marder, X. Zhan, J. Am. Chem. Soc. 138 (2016) 4955−4961; (g) S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 29 (2016) 9423−9429.
TE D
[16] (a) H. Yao, Y. Chen, Y. Qin, R. Yu, Y. Cui, B. Yang, S. Li, K. Zhang, J. Hou, Adv. Mater. 28 (2016) 8283–8287; (b) Y. Qin, Y. Chen, Y. Cui, S. Zhang, H. Yao, J. Huang, W. Li, Z. Zheng, J. Hou, Adv. Mater. 29 (2017) 1606340; (c) W. Zhao, S. Li, H. Yao,
EP
S. Zhang, Y. Zhang, B. Yang, J. Hou, J. Am. Chem. Soc. 139 (2017) 7148−7151; (d) Y.
AC C
Cui, H. Yao, B. Gao, Y. Qin, S. Zhang, B. Yang, C. He, B. Xu, J. Hou, J. Am. Chem. Soc. 139 (2017) 7302−7309; (e) N. Qiu, H. Zhang, X. Wan, C. Li, X. Ke, H. Feng, B. Kan, H. Zhang, Q. Zhang, Y. Lu, Y. Chen, Adv. Mater. 29 (2017) 1604964; (f) B. Kan, H. Feng, X. Wan, F. Liu, X. Ke, Y. Wang, Y. Wang, H. Zhang, C. Li, J. Hou, Y. Chen, J. Am. Chem. Soc. 139 (2017) 4929−4934. [17] (a) J. Zhu, Z. Ke, Q. Zhang, J. Wang, S. Dai, Y. Wu, Y. Xu, Y. Lin, W. Ma, W. You, X. Zhan, Adv. Mater. 30 (2018) 1704713; (b) Y. Duan, X. Xu, H. Yan, W. Wu, Z. 25
ACCEPTED MANUSCRIPT Li, Q. Peng, Adv. Mater. 29 (2017) 1605115; (c) W. Jiang, R. Yu, Z. Liu, R. Peng, D. Mi, L. Hong, Q. Wei, J. Hou, Y. Kuang, Z. Ge, Adv. Mater. 30 (2018) 1703005; (d) J. Zhang, Y. Li, J. Huang, H. Hu, G. Zhang, T. Ma, P.C.Y. Chow, H. Ade, D. Pan, H. Yan,
RI PT
J. Am. Chem. Soc. 139 (2017) 16092–16095; (e) B. Kan, H. Feng, X. Wan, F. Liu, X. Ke, Y. Wang, Y. Wang, H. Zhang, C. Li, J. Hou, Y. Chen, J. Am. Chem. Soc. 139 (2017) 4929−4934; (f) H. Li, Z. Xiao, L. Ding and J. Wang, Sci. Bull. 63 (2018)
SC
340–342.
M AN U
[18] (a) J.E. Coughlin, Z.B. Henson, G.C. Welch, G. . Bazan, Acc. Chem. Res. 47 (2014) 257–270; (b) Y. Chen, X.J. Wan, G. Long, Acc. Chem. Res. 46 (2013) 2645–2655; (c) J.E. Coughlin, Z.B. Henson, G.C. Welch, G.C. Bazan, Acc. Chem. Res. 47 (2014) 257–270.
TE D
[19] (a) S. Zhang, L. Yang, D. Liu, C. He, J. Zhang, Y. Zhang, J. Hou, Sci. China Chem. 60 (2017) 1340–1348; (b) J.-L. Wang, K.-K. Liu, J. Yan, Z. Wu, F. Liu, F. Xiao,
7687–7697.
EP
Z.-F. Chang, H.-B. Wu, Y. Cao, T.P. Russell, J. Am. Chem. Soc. 138 (2016)
AC C
[20] K. Wang, B. Guo, Z. Xu, X. Guo, M. Zhang, Y. Li, ACS Appl. Mater. Interfaces 7 (2015) 24686−24693.
[21] (a) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang, J. Hou, Chem. Rev. 116 (2016) 7397–7457; (b) J. Hou, M.H. Park, S. Zhang, Y. Yao, L. Chen, J. Li, Y. Yang, Macromol. 41 (2008) 6012−6018; (c) L. Ye, S. Zhang, L. Huo, M. Zhang, J. Hou, Acc. Chem. Res. 47 (2014) 1595−1603. [22] (a) M. Zhang, X. Guo, W. Ma, S. Zhang, L. Huo, H. Ade, J. Hou, Adv. Mater. 26 (2014) 2089–2095; (b) M. Zhang, Y. Gu, X. Guo, F. Liu, S. Zhang, L. Huo, T.P. 26
ACCEPTED MANUSCRIPT Russell, J. Hou, Adv. Mater. 25 (2013) 4944–4949; (c) M. Zhang, X. Guo, W. Ma, H. Ade, J. Hou, Adv. Mater. 27 (2015) 4655–4660; (d) C. Cui, W.-Y. Wong, Y. Li, Energy Environ. Sci. 7 (2014) 2276. [23] (a) H. Son, W. Wang, T. Xu, Y. Liang, Y. Wu, G. Li, L. Yu, J. Am. Chem. Soc.
RI PT
133 (2011) 1885−1894; (b) M. Zhang, X. Guo, S. Zhang, J. Hou, Adv. Mater. 26 (2014) 1118−1123.
[24] (a) G.C. Welch, L.A. Perez, C.V. Hoven, Y. Zhang, X.-D. Dang, A. Sharenko,
SC
M. F. Toney, E.J. Kramer, T.-Q. Nguyen, G.C. Bazan, J. Mater. Chem. 21 (2011) 12700–12709; (b) Z.B. Henson, G.C. Welch, T. Poll, G.C. Bazan, J. Am. Chem. Soc.
M AN U
134 (2012) 3766−3779; (c) J. Wolf, M. Babics, K. Wang, Q. Saleem, R.-Z. Liang, M. R. Hansen, P.M. Beaujuge, Chem. Mater. 28 (2016) 2058–2066. [25] T.S. Poll, J.A. Love, T.-Q. Nguyen, G.C. Bazan, Adv. Mater. 24 (2012) 3646–3649.
TE D
[26] (a) Y. Sun, G.C. Welch, W.L. Leong, C.J. Takacs, G.C. Bazan, A.J. Heeger, Nat. Mater. 11 (2011) 44–48; (b) D. Qian, W. Ma, Z. Li, X. Guo, S. Zhang, L. Ye, H. Ade, Z. Tan, J. Hou, J. Am. Chem. Soc. 135 (2013) 8464−8467; (c) J. Zhou, Y. Zuo, X.
EP
Wan, G. Long, Q. Zhang, W. Ni, Y. Liu, Z. Li, G. He, C. Li, B. Kan, M. Li, Y. Chen,
AC C
J. Am. Chem. Soc. 135 (2013) 8484−8487; (d) S. Shen, P. Jiang, C. He, J. Zhang, P. Shen, Y. Zhang, Y. Yi, Z. Zhang, Z. Li, Y. Li, Chem. Mater. 25 (2013) 2274−2281. [27] (a) M. M. Mandoc, W. Veurman, L. J. A. Koster, B. Boer, P. W. M. Blom, Adv. Funct. Mater. 17 (2007) 2167–2173; (b) C. M. Proctor, J. A. Love, T.-Q. Nguyen, Adv. Mater. 26 (2014) 5957–5961. [28] (a) B. Guo, W. Li, X. Guo, X. Meng, W. Ma, M. Zhang, Y. Li, Adv. Mater. 29 (2017) 1702291; (b) H. Yao, L. Ye, J. Hou, B. Jang, G. Han, Y. Cui, G.M. Su, C. Wang, B. Gao, R. Yu, H. Zhang, Y. Yi, H.Y. Woo, H. Ade, J. Hou, Adv. Mater. 29 27
ACCEPTED MANUSCRIPT (2017) 1700254; (c) C. M. Proctor, M. Kuik, T.-Q. Nguyen, Prog. Polym. Sci. 38 (2013) 1941−1960; (d) C.Z. Li, C.Y. Chang, Y. Zang, H.X. Ju, C.C. Chueh, P.W. Liang, N. Cho, D.S. Ginger, A.K. Jen, Adv. Mater. 26 (2014) 6262−6267; (e) B. Qiu,
Zhang, Y. Li, Chem. Mater. 29 (2017) 7543–7553.
RI PT
L. Xue, Y. Yang, H. Bin, Y. Zhang, C. Zhang, M. Xiao, K. Park, W. Morrison, Z.-G.
[29] J.-L. Wu, F.-C. Chen, Y.-S. Hsiao, F.-C. Chien, P. Chen, C.-H. Kuo, M.H. Huang, C.-S. Hsu, ACS Nano 5 (2011) 959–967.
SC
[30] (a) Y.-J. Hwang, H. Li, B.A.E. Courtright, S. Subramaniyan, S.A. Jenekhe, Adv.
M AN U
Mater. 28 (2016) 124–131; (b) M. Lenes, M. Morana, C.J. Brabec, P.W.M. Blom, Adv. Funct. Mater. 19 (2009) 1106–1111; (c) P. Schilinsky, C. Waldauf, C.J. Brabec, Appl. Phys. Lett. 81 (2002) 3885.
[31] L.J.A. Koster, V.D. Mihailetchi, R. Ramaker, P.W.M. Blom, Appl. Phys. Lett. 86 (2005) 123509.
TE D
[32] K. Wang , X. Guo , B. Guo , W. Li , M. Zhang , Y. Li, Macromol. Rapid
AC C
EP
Commun. 37 (2016) 1066−1073.
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Highlights： ： 1. BDTDPTz with A-D-A structured was synthesized for the application in Solar Cells.
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2. The OSCs shows a PCE of 6.28% with a lower PC71BM content of 40%.
3. PC71BM content of 40% is one of the lowest acceptor content in the
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active layer.
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solution-processable OSCs.
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4. BDTDPTz could be promising high performance donor in